Reflection type liquid crystal display device and manufacturing method thereof

ABSTRACT

The present invention is a method of manufacturing a liquid crystal display device, wherein light having an exposure energy is irradiated on the surface of a photo-sensitive resin layer having a predetermined film thickness, and a distribution of thermal deformation characteristics in the thickness direction (or the plane direction) of the photo-sensitive resin layer is formed, then heat treatment is performed to form random undulation (micro-grooves or micro-wrinkles) on the surface of the photo-sensitive resin layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 10/698,994, filedOct. 31, 2003, which is a continuation-in-part of prior application Ser.No. 10/051,709 filed on Jan. 18, 2002, which is now U.S. Pat. No.6,882,388, issued Apr. 19, 2005. This application is based upon andclaims the benefit of priority from the prior Japanese PatentApplication No. 2001-16882, filed on Jan. 25, 2001, No. 2001-101755,filed on Mar. 30, 2001, No. 2002-318657, filed on Oct. 31, 2002, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflection type liquid crystaldisplay device and a manufacturing method thereof, and more particularlyto a reflection type liquid crystal display device having a scatteringreflector structure with high reflectance by a simple process, and amanufacturing method thereof.

2. Description of the Related Art

Recently in liquid crystal panels using an active matrix, reflectionliquid crystal display devices, which can implement light weight,slimness and low power consumption, are attracting attention. Areflection type liquid crystal display device can decrease powerconsumption since light from the outside is taken inside the displaypanel and is reflected by a reflector installed at the rear face side,and backlight is unnecessary. Therefore the reflection type liquidcrystal display device is useful as a display device for portableinformation terminals and portable telephones.

Light from the outside differs depending on the environment where thedisplay device is used. Therefore it is desirable that the reflectorinstalled in the display panel have a light scattering reflectionstructure which reflects light entering from a random direction to arandom direction.

As such a reflection liquid crystal display device, a structure wherepixel electrodes are formed on a bumpy shape film so that external lightis irregularly reflected by the bumpy pixel electrodes has beenproposed. For example, Japanese Patent Laid-Open No. H5-232465 andJapanese Patent Laid-Open No. H8-338993 proposed this structure. Thereflection liquid crystal display device described in these publicationsuses photo-lithography processing using a mask pattern, or uses acombination of a polishing process and etching process in order to formundulation for pixel electrodes.

In these prior arts, high reflectance can be obtained by forming anarbitrary bump pattern at reflection electrodes.

But to control the shape of reflection electrodes usingphoto-lithography makes the process complicated. Since reflectioncharacteristics change considerably if shape changes depending on theexposure conditions, the margin in the manufacturing process is small.

As a method of solving this problem, Japanese Patent Laid-Open No.H5-80327 discloses a method of simplifying the process using a thin filmresin layer where the coefficient of thermal expansion is different fromthat of the reflection electrodes. With this method, however, undulationis formed on the surface of the pixel electrodes by forming a metal filmby a heat sputtering method after organic film is formed. This methodgenerates degassing from the organic film during the heating process ina vacuum, causing a change in the film quality of the reflection film orgenerating small undulation on the reflection film, which drops thereflection characteristics, therefore this process is not practical.

Japanese Patent Laid-Open 2000-193807 proposes a technology for formingfine undulation on organic films using fluorine-contained resin having afluorine aliphatic ring structure for the main chain. This method,however, must use special resin, and requires a baking process at a hightemperature of 350° C. Also, as the known example shows, this resinitself does not have photo-sensitivity, so if undulation is formed onpixel electrodes to be connected to a thin film transistor, resin mustbe coated separately to generate contact holes in the photo-lithographyprocess, which makes the process complicated.

Also Japanese Patent Laid-Open No. H10-253977 states that undulationhaving variable distribution in the depth direction are formed using theintensity distribution of speckles which are generated when a coherentlight is irradiated, so as to form a reflector having random bumpdistribution. This method, however, requires a special exposure system,and this exposure system is huge and has a high cost, which means thatthis method is not practical.

A plurality of undulation is formed at the surface of reflectiveelectrodes of reflection type liquid-crystal devices in order to improvethe optical scattering characteristic. Typically, in order to form theundulations at the surface of the reflective electrodes, the undulationsare formed in the surface of the underlayer of the reflectiveelectrodes. In this way, the undulations imitating the undulations ofthe underlayer are formed in the reflective electrodes.

An etching technique, of performing etching so as to produce a sinewave-shaped or triangular wave-shaped cross-sectional shape of thesurface of an underlayer made of silicon oxide film (SiO₂ film) is aknown method of forming the undulations in the underlayer (see forexample Laid-open Japanese Patent Application No. S56-156864 andLaid-open Japanese Patent Application No. S56-156865).

The following other techniques are known as methods of forming theundulations in the underlayer. First of all, a layer of photocured resinis formed as the underlayer. Next, the photocured resin layer is exposedusing a photo-mask, in which a plurality of transparent regions areprovided, for formation of the undulations. A photo-polymerizationreaction is promoted in the exposed portions of the photocured resinlayer, causing them to swell up relative to the unexposed portions,thereby forming raised portions. Next, further exposure of thephotocured resin layer is performed using a photo-mask for contact holeformation. In this way, the photocured resin layer in the regions otherthan the regions where the contact holes are to be formed is cured,forming a plurality of the undulations in the surface. The contact holesare formed by subsequent development (see for example Laid-open JapanesePatent Application No. H11-153804).

In addition, the following technique is known as a method of forming theundulations in the underlayer. First of all, an underlayer is formed bycoating photosensitive resin onto a substrate. Next, the photosensitiveresin on the substrate is heated to partially different temperaturesusing a baking treatment device having a special hotplate. Solvent isevaporated from regions of the photosensitive resin that are heated tocomparatively high temperature, decreasing its film thickness andresulting in the formation of surface undulations. The surfaceundulations of the photosensitive resin are maintained by performingbaking treatment for a prescribed time. After this, an underlayer ofundulated surface shape is formed through an exposure step anddevelopment step, using a photo-mask (see for example Laid-open JapanesePatent Application No. 2001-67017).

As a material used for an underlayer, a coating agent is also knowncontaining a dye having a UV-absorbing capability (see for exampleLaid-open Japanese Patent Application No. 2001-348514). If such acoating agent is employed as the underlayer, UV is absorbed by the dye,so only the surface portions of the underlayer are cured by the UVirradiation and other portions of the surface of the underlayer are notcured. A difference between the surface portion and underlayer portionin the amount of shrinkage on curing is produced by heat, so theundulations are formed in the surface of the underlayer by subsequentheat treatment.

In addition, two Japanese Patent Applications (see Laid-open JapanesePatent Application No. 2002-296585, 2002-221716) filed by the presentapplicants proposes a technique for forming surface undulations of theunderlayer by directing light of prescribed exposure energy onto thesurface of the underlayer and subsequently performing heat treatment ofthe underlayer. These Japanese Applications are the corresponding onesof the co-pending parent U.S. patent application Ser. No. 10/051,709assigned to the same assignee.

However, if SiO₂ film is employed for the underlayer, a separatedeposition process is required. Also, even if photosensitive resin isemployed for the underlayer, either a new photo-mask is needed in theabove technique, or a special manufacturing device or resin material isrequired.

Consequently, there is the problem that the manufacturing step of theliquid-crystal display device becomes complicated, increasingmanufacturing costs.

A further problem is that the undulations are not reliably formed in thesurface of the underlayer even by a method of irradiating the surface ofthe underlayer with light of a prescribed exposure energy andsubsequently performing heat treatment [,as discussed in the above twoJapanese Patent Applications].

As described above, various reflection type liquid crystal displaydevices where a scattering reflection electrode is used for a pixelelectrode have been proposed, but in all cases, a scattering reflectionelectrode having sufficient reflectance cannot be formed with a simplemanufacturing process. In order to form an optimum reflection electrodestructure, it is necessary to control the average inclination angle ofthe undulation and the inclination angle distribution in an optimumrange, but no manufacturing process which can control the averageinclination and the inclination angle distribution to be an optimumreflection electrode structure with good repeatability has beenproposed.

Also the inclination angle of the undulation of the reflector of aconventional reflection liquid crystal display device is selected suchthat maximum reflectance is obtained with respect to an incident lightfrom a specific direction. A conventional reflector requires setting theinclination angle of the undulation to be 10°-20°, for example (JapanesePatent Laid-Open No. H11-259018), setting the inclination angle of theundulation of the reflector to be a uniform angle in a 5°-25° range(Japanese Patent Laid-Open No. H08-227071), setting the averageinclination angle of the undulation of the reflector to be 30° or less(Japanese Patent Laid-Open No. S56-156865), with the heights ofundulation in Gaussian distribution and the average inclination angle ofthe undulation at this time 10° (Tohru Koizumi and Tatsuo Uchida,Proceedings of the SID, Vol. 29, p. 157, 1988), and the surface of thereflector having a smooth bump face, and the average inclination angleof the undulation 4°-15° (Japanese Patent Laid-Open No. H6-175126).

In these prior arts however, no consideration was made concerningwhether the reflectance becomes highest no matter from which directionthe external lights enter the display panel. Therefore in the priorarts, no reflection type liquid crystal display device which becomesbright where external light is reflected at high reflectance undervarious environments have been proposed.

Also none of the prior arts proposed undulation shapes to makereflectance high, assuming a case when external lights enter the displaypanel of a notebook computer from all orientations at a certaindirection and from a specific orientation at a direction which isdifferent from that.

A reflector structure where a resist film is formed, exposed anddeveloped with a predetermined mask pattern, then the cross-sectionalstructure of the resist film is smoothed by a baking process, so as toform a desired inclined face, has been proposed. However, in such amanufacturing process, an optimum pattern shape has not been proposed. Amethod of forming a undulation shape for reflection which has bothdirectivity and scattering properties in a same pixel area has also notbeen proposed.

Also a reflection liquid crystal display device, which uses externallights, requires a light source to be used in a dark place. However, ifa structure, where light from the light source is scattered and enteredinto the display panel side, is used, the displayed image is blurred bythis scattering structure, which aggravates contrast.

The reflection type liquid crystal display device, which does not usebacklight, can be slim, light and have low power consumption.

The reflection liquid crystal display device is roughly comprised ofthree layers, that is, a light shutter layer, a colored layer and alight reflection layer, but it is most important to obtain a brightdisplay by utilizing ambient light efficiently. The light reflectionlayer of the above three layers has a particularly large influence notonly on light utilization efficiency but also on viewing anglecharacteristics. Therefore optimizing the light reflection layer is mostimportant to implement a bright reflection liquid crystal displaydevice, and obtaining a bright light reflection layer has beenconsidered.

Also a reflection type liquid crystal display device having a frontlight structure as an illumination system has been developed.

Also, by using a guest-host system where dichroic dye are mixed or a onepolarizer system where one polarizer is used for the light shutterlayer, a very bright display can be obtained in the former, and veryhigh contrast can be obtained in the latter respectively in a brightstate.

When the guest-host system where dichroic dye are mixed is used for thelight shutter layer, considerable light leaks are generated if a diffusereflector with high reflection efficiency is used, since the contrast ofthe guest-host liquid crystal is low in the dark state. In this state,the value of contrast of display characteristics is good, but thedisplay does not look good visually.

Also if one diffuse reflector and one polarizer system are combined fora display, in this case, the display is good in the dark state, butbrightness becomes insufficient in the bright state because of lightabsorption by the polarizer.

In the case of a reflection type liquid crystal display device having afront light structure as an illumination device, there are manyinterfaces between the liquid crystal substrate and the light guidingplate of the front light structure, therefore the light guided by thelight guiding plate and the light directly entered from the outside isreflected at the interface without reaching the liquid crystalsubstrate. The light reflection which does not contribute to the liquidcrystal display causes a drop in display quality, especially incontrast. Also, a reflection type liquid crystal display deviceprimarily used for PDA normally has a touch panel on the surface. Whenthe display device has a touch panel, there are also interface betweenthe touch panel and the light guiding plate, therefore the abovementioned drop in contrast aggravates. Therefore it has been difficultto implement a reflection type liquid crystal panel having both a frontlight and a touch panel. As a countermeasure, a structure to decreasethe reflection interfaces by integrating the light guiding plate of thefront light structure and the touch panel has been considered, but thetransparent conductive film used for the touch panel absorbs specificbands (blue and red, B, R) of the light being guided by the lightguiding plate, and green becomes dominant on screen when combined withthe light guiding plate.

Also, in the case of a prism type light guiding plate, a leak lightcomponent, which is directly emitted from the light guiding plate to theobserver, is generated, which drops the contrast and makes particleswhich adhere to the surface of the prism more outstanding. Thiscomponent is transmitted from the steep slope side of the prism face ofthe light guiding plate, which can be shielded to some extent, but theprism face of the light guiding plate is also a face where panelillumination light is generated, and it is difficult to implement boththe shielding light to prevent leak light and panel illumination.

In this way, the reflection type liquid crystal display device can beslim, light weight and have low power consumption, but has seriousproblems due to a complicated manufacturing process and a narrowing ofthe manufacturing process margins, and it is difficult to improve thereflection characteristics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method ofmanufacturing a substrate for a liquid-crystal display device wherebyexcellent surface characteristics can be obtained even though themanufacturing step is simplified, and a method of manufacturing aliquid-crystal display device using this.

The foregoing object is achieved by a method of manufacturing asubstrate for a liquid-crystal display device comprising the steps offorming a resin layer on a substrate, selective reforming the surfaceportion of the resin layer by applying energy with an energy density perunit time of a prescribed value or more to the resin layer to generate adifference in the rate of thermal shrinkage between the surface portionand the underlayer portion other than the surface portion, performing aheat treatment to the resin layer to form the undulations in the surfaceportion, and forming reflective electrode on the surface portion.

According to the above aspect of the invention, since the energy densityper unit time (mW/cm²) is relatively larger, the surface of the resinlayer can be selectively reformed, even though the resin layer is hardenor semi-harden before the energy application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of a circuit diagram of a liquid crystal displaydevice to which the present embodiment is applied;

FIG. 2 is a diagram depicting an example of a cross-sectional view of areflection type liquid crystal display device to which the presentembodiment is applied;

FIG. 3 is a cross-sectional view depicting a part of the manufacturingprocess of a reflection type crystal display device of the presentembodiment;

FIG. 4 is a micro-photograph of the surface shape of the micro-groovesof a reflection panel which is created by changing the film thickness ofthe photo-sensitive resin layer 20 and the UV irradiation energy;

FIG. 5 is a micro-photograph of the surface shape of the micro-groovesof a reflection panel which is created by changing the film thickness ofthe photo-sensitive resin layer 20 and the UV irradiation energy;

FIG. 6 is a micro-photograph of the surface shape of the micro-groovesof a reflection panel which is created by changing the film thickness ofthe photo-sensitive resin layer 20 and the UV irradiation energy;

FIG. 7 is a micro-photograph of the surface shape of the micro-groovesof a reflection panel which is created by changing the film thickness ofthe photo-sensitive resin layer 20 and the UV irradiation energy;

FIG. 8 shows diagrams depicting AFM images of the three reflection panelsamples;

FIG. 9 is a graph depicting the relationship between the averageinclination angle of the reflection film and the reflectance withrespect to the diffuse light source;

FIG. 10 is a graph depicting the relationship between the resist filmthickness and the reflectance of the three samples in FIG. 8;

FIG. 11 shows diagrams depicting the bump shapes of the micro-grooves ofthe resin layer formed by the present embodiment;

FIG. 12 shows diagrams depicting examples of the plane pattern of themicro-groove formed by the present embodiment;

FIG. 13 shows diagrams depicting examples of the UV irradiation requiredto form micro-grooves;

FIG. 14 shows cross-sectional views depicting the manufacturing processof the first sample;

FIG. 15 is a graph comparing the reflectance of the diffuse light sourceof an integrating sphere on the first, second and third samples;

FIG. 16 shows diagrams depicting the separation of the photo-sensitiveresin layer;

FIG. 17 shows cross-sectional views depicting the process of formingseparation lines of the photo-sensitive resin layer;

FIG. 18 shows micro-graphs of micro-grooves when separation lines areformed and when not formed;

FIG. 19 is a diagram depicting an actual environment where a reflectiontype liquid crystal display device, which the present embodimentassumes, is used;

FIG. 20 shows diagrams depicting the incident angle θi and azimuth angleφ1;

FIG. 21 is a diagram depicting the case when light enters the reflectiondisplay device and is reflected;

FIG. 22 is a diagram depicting the relationship between intensity f(θ_(i)′) and incident angle θ_(i)′ of light entered into the reflector;

FIG. 23 is a diagram depicting the relationship between the incidentangle θ_(i)′, when the incident light intensity of FIG. 22 is at themaximum and refractive index n of the medium;

FIG. 24 is a diagram depicting the relationship of the incident angle,reflection angle and inclination angle with respect to the inclined faceof the reflection undulation;

FIG. 25 is a diagram depicting the distribution of the existenceprobability of the inclination angle corresponding to the incident lightintensity distribution in FIG. 22;

FIG. 26 is a diagram depicting the simulation result of reflectioncharacteristics;

FIG. 27 is a diagram depicting the result of measuring reflectance withrespect to the uniform diffused light of an integrating sphere using anactual prototype sample;

FIG. 28 is a cross-sectional view depicting a method of forming thereflector prototype;

FIG. 29 shows diagrams depicting examples of the pattern of the mask 64for forming undulation of the reflector;

FIG. 30 is a diagram depicting the distribution of the inclinationangles of the undulation of the reflector to obtain high reflectancewith respect to the diffused light of the integrating sphere;

FIG. 31 is a diagram depicting a state when the reflection type liquidcrystal display device is mounted as a monitor of a notebook personalcomputer;

FIG. 32 is a diagram depicting the distribution of the inclinationangles in the XY plane direction and XZ plane direction having highreflectance when the reflection type liquid crystal device is used as adisplay device of a notebook personal computer;

FIG. 33 is a diagram depicting the distribution when the inclinationangle distribution in FIG. 32 is folded at the inclination angle 0° asthe center;

FIG. 34 shows cross-sectional views depicting a method of forming areflector sample;

FIG. 35 shows diagrams depicting examples of the mask patterns in FIG.34;

FIG. 36 is a plan view and cross-sectional view depicting an example ofthe convex part in FIG. 34;

FIG. 37 shows the measurement result of the inclination angledistribution of the reflector prototype;

FIG. 38 is a rough cross-sectional view of the reflection type liquidcrystal display device created using the reflector prototype;

FIG. 39 shows the measurement result of the reflectance of thereflection liquid crystal display device in FIG. 38;

FIG. 40 is a diagram depicting the inclination angle of a reflectiontype liquid crystal display device, and the inclination angle range whenthe existence probability becomes the maximum with respect to therefractive index of the liquid crystal layer;

FIG. 41 is a cross-sectional view depicting two reflection bump shapescoexisting in a pixel area;

FIG. 42 is a plan view of the pixel area PK in the present embodiment;

FIG. 43 shows cross-sectional views depicting the manufacturing processfor forming the undulation for reflection in FIG. 42;

FIG. 44 is a diagram depicting a circular pattern example of aconventional resist;

FIG. 45 is a diagram depicting a circular pattern example of resist inthe present embodiment;

FIG. 46 shows diagrams depicting the circular pattern in FIG. 45;

FIG. 47 is a diagram depicting a polygon pattern example of resist inthe present embodiment;

FIG. 48 is a diagram depicting a polygon pattern example of resist inthe present embodiment;

FIG. 49 is a diagram depicting the configuration of a conventionallyproposed reflection type liquid crystal display panel with a frontlight;

FIG. 50 shows diagrams depicting a first example of a reflection typeliquid crystal display panel with front light;

FIG. 51 shows diagrams depicting a second example of a reflection typeliquid crystal display panel with front light;

FIG. 52 shows diagrams depicting a third example of a reflection typeliquid crystal display panel with front light;

FIG. 53 shows diagrams depicting a fourth example of a reflection typeliquid crystal display panel with front light;

FIG. 54 shows diagrams depicting a fifth example of a reflection typeliquid crystal display panel with front light;

FIG. 55 shows a diagram depicting a sixth example of a reflection typeliquid crystal display panel with front light;

FIG. 56 show a diagram depicting a seventh example of a reflection typeliquid crystal display panel with front light;

FIG. 57 shows cross-sectional views depicting a conventionalmanufacturing process and the manufacturing process of the presentinvention of the bump formation method;

FIG. 58 shows cross-sectional views depicting a conventional maskpattern and the mask pattern of the present invention of the bumpformation method;

FIG. 59 shows micro-photographs showing an example of micro-grooveformation when block separation was formed by half exposure;

FIG. 60 is a micro-photograph which shows the micro-grooves formed inthe fabrication example 4;

FIG. 61 is a micro-photograph of one polarizer type TFT drivenreflection liquid crystal device fabricated using CF substrate and a TFTsubstrate where a pixel electrode is formed on the substrate bysputtering and photo-lithograph Al electrode;

FIG. 62 shows plan views depicting the state of controlling the shape ofmicro-grooves by controlling the arrangement and shape of the electrodelayer, including the gate electrode, Cs electrode and data electrode,and the inter-layer insulation film layer;

FIG. 63 shows plan views depicting the state of controlling the bumpshapes on the surface of a reflection electrode by size, shape,arrangement and number of contact holes for electrically connecting thedrain electrode and the reflection electrode;

FIG. 64 is a cross-sectional view depicting a rough configuration of theresin layer of the fabrication example 1;

FIG. 65 is a cross-sectional view depicting a rough configuration of theresin layer of the fabrication example 2;

FIG. 66 is a cross-sectional view depicting a rough configuration of theresin layer of the fabrication example 3;

FIG. 67 is a cross-sectional view depicting a rough configuration of theresin layer of the fabrication example 4;

FIG. 68 is a schematic diagram depicting a rough configuration of theresin layer of the fabrication example 1;

FIG. 69 is a schematic diagram depicting the influence of the shrinkagefactor on bump shape;

FIG. 70 is a schematic diagram depicting an example of cross-link by theoxidation of novolak;

FIG. 71 is a micro-photograph of the resist surface;

FIG. 72 is a characteristic diagram depicting the result of examiningthe state of undulation being generated on the resist surface;

FIG. 73 is a characteristic diagram depicting the result of examiningthe state of generating undulation when the bake temperature is changedbefore UV irradiation and after UV irradiation;

FIG. 74 is a micro-photograph showing the state of bubbles generated onthe resist;

FIG. 75 shows micro-photographs showing the resist surface;

FIG. 76 is a characteristic diagram depicting the result of measuringreflectance;

FIG. 77 is a cross-section view depicting a rough configuration of afabricated liquid crystal cell;

FIG. 78 is a characteristic diagram depicting the result of measuringreflectance when applied voltage is changed using an integrating sphere;

FIG. 79 shows micro-photographs showing patterned substrates afterbaking;

FIG. 80 shows micro-photographs showing substrates where 80 mJ/cm² and35 mJ/cm² were irradiated;

FIG. 81 is a perspective view depicting a glass substrate;

FIG. 82 shows micro-photographs showing micro-shapes generated afterbaking;

FIG. 83 shows plan views depicting the patterns of the diffuse reflectorof the fabrication example 1;

FIG. 84 shows characteristic diagrams depicting the result of measuringreflection characteristics;

FIG. 85 is a characteristic diagram depicting the result of examiningthe relationship of the twist angle and reflectance of the liquidcrystal layer;

FIG. 86 is a characteristic diagram depicting the result of examiningthe viewing angle characteristic in a bright state and dark state of areflection guest-host liquid crystal;

FIG. 87 is a schematic diagram depicting a guest-host liquid crystaltwisted at 180°;

FIG. 88 is a characteristic diagram depicting the reflectioncharacteristics of a polarizer;

FIG. 89 is a cross-sectional view depicting a rough configuration of afabricated one polarizer type reflection liquid crystal display device;

FIG. 90 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example1;

FIG. 91 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example2;

FIG. 92 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example3;

FIG. 93 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example3;

FIG. 94 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example4;

FIG. 95 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example5;

FIG. 96 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example6;

FIG. 97 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example6;

FIG. 98 is a cross-sectional view depicting the structure of ascattering directivity element;

FIG. 99 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example6;

FIG. 100 is a cross-sectional view depicting a rough configuration ofthe reflection type liquid crystal display device of the fabricationexample 6;

FIG. 101 is a cross-sectional view depicting a rough configuration ofthe reflection type liquid crystal display device of the comparisonexample; and

FIG. 102 is a cross-sectional view depicting a conventional reflectionliquid type crystal display device with a front light structure.

FIG. 103 is a view showing the diagrammatic layout of a reflective typeliquid-crystal display device manufactured using a method ofmanufacturing a liquid-crystal display device according to an embodimentof the present invention;

FIG. 104 is a view showing the layout of a substrate for aliquid-crystal display device manufactured using a method ofmanufacturing a substrate for a liquid-crystal display device accordingto an embodiment of the present invention;

FIG. 105 is a view showing the layout of a substrate for aliquid-crystal display device manufactured using a method ofmanufacturing a substrate for a liquid-crystal display device accordingto an embodiment of the present invention;

FIG. 106 is a photomicrograph of a substrate for a liquid-crystaldisplay device manufactured using a method of manufacturing a substratefor a liquid-crystal display device according to an embodiment of thepresent invention;

FIG. 107 is a table showing the relationship between the treatmentconditions in the various steps of the method of manufacturing asubstrate for a liquid-crystal display device according to an embodimentof the present invention and the presence of wrinkle-shaped surface theundulations of the reflective electrode surface;

FIG. 108 is a process cross-sectional view showing a method ofmanufacturing a substrate for a liquid-crystal display device accordingto an embodiment of the present invention;

FIG. 109 is a process cross-sectional view showing a method ofmanufacturing a substrate for a liquid-crystal display device accordingto an embodiment of the present invention; and

FIG. 110 is a process cross-sectional view showing a method ofmanufacturing a substrate for a liquid-crystal display device accordingto an embodiment of the present invention

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described withreference to the accompanying drawings. The embodiments, however, do notlimit the technical scope of the present invention.

FIG. 1 is an example of a circuit diagram of a liquid crystal displaydevice to which the present embodiment is applied. Pixels are created ina matrix in a display area 11 of the insulation substrate 10 at the rearface side. The pixels have drive transistors T00-Tmn and pixelelectrodes P00-Pmn, and the drive transistors T00-Tmn are connected tothe scanning lines S0-Sm arranged in a row direction, and to the datalines D0-Dn arranged in a column direction respectively. Outside thedisplay area 11, the scanning line drive circuit 12 for driving thescanning lines and the data line drive circuit 13 for driving the datalines are disposed.

FIG. 2 is a diagram depicting an example of a cross-sectional view of areflection type liquid crystal display device to which the presentembodiment is applied. The structure of the reflection type liquidcrystal display device is that the liquid crystal layer 34 is disposedbetween the insulation substrate 10 at the rear face side and thetransparent substrate 30 at the display side, where the reflectionelectrode 22 is formed on the insulation substrate 10 at the rear faceside, and external light entered from the display side is reflected onthe surface of the reflection electrode 22, transmits the liquid crystallayer 34 and is emitted to the display side again.

On the insulation substrate 10, the gate electrode 15 to be connected tothe scanning line, which is not illustrated, the insulation layer 16,the semiconductor layer 19, and the drain electrode 17 and the sourceelectrode 18 to be connected to the data line, are formed. Also on theresin layer 20 of the inter-layer insulation film, the reflectionelectrode 22, which is the pixel electrode, is formed, and thereflection electrode 22 is connected to the source electrode 18 via thecontact hole CH. On the resin layer 20 and the reflection electrode 22,the alignment film 23, comprised of polyimide, is formed. At the surfaceof the resin layer 22, random undulation to irregularly reflect incidentlight, are formed, and random undulation is also formed on the surfaceof the pixel electrode (reflection electrode) 22, which is depositedthereon.

On the entire surface of the transparent substrate 30 at the displayside, the transparent electrode 31 comprised of ITO (material which maincomponent is indium oxide) and the alignment film 32, are formed on oneside and the polarizer 33 on the other. The liquid crystal layer 34 isinserted between the alignment film 32 at the display side and thealignment film 23 at the rear face side. The alignment direction of theliquid crystal molecules of the liquid crystal layer 34 depends on thesurface shape of the alignment films 32 and 23, and on thecharacteristics thereof.

[Method of Forming Micro-Grooves]

FIG. 3 shows cross-sectional views depicting a part of the manufacturingprocess of a reflection type liquid crystal display device according tothe present embodiment. FIG. 3 shows a part of the source electrode 18of the thin film transistor shown in FIG. 2. As FIG. 3A shows, afterforming the insulation layer 16, each electrode of the thin filmtransistor, and the semi-conductive layer on the insulation substrate10, and the photo-sensitive resin 20, such as LC-200 (novolak resin),which is a general purpose resist made by Shipley Co., is coated. Theresin layer 20 is spin coated by a spinner to be about a 0.5-4.0 μm infilm thickness. The spin coating method in this case involves, forexample, forming resist layer by 2 steps for a 3 second spin coating ata rotation frequency of about 350 rpm, and a 20 second spin coating at arotation frequency of about 800 rpm.

The film thickness of the resin layer 20 influences roughness (heightdifference and pitch length) of the undulation of the micro-groovesformed on the surface, so an appropriate film thickness is selected. Asmentioned later, as the film thickness of the photo-sensitive resinlayer 20 increases, the undulation become rougher (large heightdifference, large pitch length), and as the film thickness decreases,the undulation become finer (small height difference, small pitchlength).

Then pre-bake processing is performed for 30 minutes at about a 90° C.temperature. In this pre-bake processing, temperature is not so highthat resist does not react, and only the solvent is eliminated. Thisprevents the later mentioned sagging of the resist layer by heat duringthe post-bake process.

As FIG. 3B shows, a known stepper exposure processing and developmentprocessing are executed using the mask substrate 40 to form a contacthole of the display electrode. As a result, the contact hole CH isformed on the source electrode 18 of the resin layer 20.

After forming the contact hole CH, post-bake processing is performed onthe photo-sensitive resin layer 20. Post-bake processing is, forexample, a heat treatment at 120° C. for 40 minutes, aiming atsufficiently eliminating the solvent of the photo-sensitive resin. Thetemperature of the post-bake processing must be lower than thetemperature at which the sensitizing agent of the photo-sensitive resinreacts (e.g. about 200° C.), so that the sensitizing agent does notreact during the post-bake processing. The temperature of the post-bakeprocessing must also be lower than the glass-transition temperature(e.g. about 160° C.) so that the resin does not harden.

As the temperature of the post-bake processing increases and the timethereof increases, the amount of residual solvent decreases and theundulation of the micro-grooves become finer, and as the temperaturedecreases and the time increases, the undulation of the micro-groovesbecome rougher. Therefore the conditions of the post-bake processing areselected so as to form the optimum shapes of the micro-grooves.

Then, as FIG. 3C shows, a light having energy sufficiently high enoughto sensitize the resin, a deep-ultraviolet radiation (DUV) with awavelength of λ=360 nm or less, for example, is irradiated on the entiresurface of the photo-sensitive resin layer 20, with an energy of about2600 mJ/cm². By this DUV irradiation, the sensitizing agent reacts andnovolak resin cross-links from the surface part of the photo-sensitiveresin layer 20 (front face side in the film thickness direction), andthe upper layer part of the resin layer is altered. As a result, thefront face side and the rear face side of the resin layer 20 becomesubstances having different thermal deformation characteristics. ThisDUV irradiation is performed using a UV irradiation system made by ORC,for example.

The energy of the UV irradiation also influences the shape of themicro-grooves. If the energy is too low, micro-grooves are not formed,but if energy exceeding a certain threshold is irradiated, micro-groovesare formed. In this case, as the irradiation energy (energy per unittime×irradiation time) decreases, the micro-grooves become finer, and asthe irradiation energy increases, the micro-grooves become rougher.Therefore the amount of irradiation energy is also selected according tothe optimum shape of the micro-grooves.

Then, as FIG. 3D shows, a final bake is performed on the resist 20. Thisheat treatment is performed at a 200° C. temperature for about 40minutes, for example. The temperature of the heat treatment in the finalbake must be higher than the temperature during the heat processing(post-bake) before UV irradiation. And by performing the heat processingin the final bake, the random micro-grooves MG are formed, asillustrated, on the surface of the resin layer 20.

The heat treatment temperature of the final bake must be equal to orhigher than a temperature for post-bake, and preferably is sufficientlyhigher than the baking temperature of the alignment film in the laterheat treatment process, so that the resin layer 20 sufficiently hardens.

Then, as FIG. 2 shows, aluminum is grown to about 2000 Å by a sputteringmethod or by a heating deposition method, and the pixel electrode 22 isformed by patterning by a known photo-lithography method. As a result,random undulation is formed on the surface of the pixel electrode 22,and functions as a reflection electrode for scattering and reflectinglights. And on the entire surface thereon, the alignment film 23comprised of about 1000 Å polyimide, for example, is formed by spincoating and baking (about 180° C.). Undulation is formed also on thesurface of this alignment film 23, and the alignment direction of liquidcrystal molecules of the liquid crystal layer 34 to be inserted thereonaligns according to the groove direction of the undulation.

The reason why micro-grooves are formed is not yet certain, butaccording to the knowledge of the inventors, the surface part of theresin layer 20 is altered by DUV irradiation, the front face side andthe rear face side of the resin layer 20 are thermally altereddifferently during the heat treatment of the final bake, andmicro-grooves or micro-wrinkles are formed on the surface by the stressbetween the top layer and the bottom layer of the resin layer 20. Forexample, micro-grooves are formed on the front face side by theshrinkage of the rear face side of the resin layer 20. This is caused bythe difference in the cross-link reaction level of the resin in thethickness direction of the resin layer due to UV irradiation.

According to an experiment of the inventors, they confirmed that themicro-grooves formed in this way have the random undulation required foran irregular reflection of the external light which enters.

UV irradiation in the above mentioned process may be performed only on apart of an area of the resin layer 20 in the plane direction using apredetermined mask pattern, instead of on the entire surface of theresin layer 20. As a result, the resin layer 20 is partially altered inthe plane direction, and the distribution of thermal deformationcharacteristics is formed in the plane direction. By such a distributionof thermal deformation characteristics in the horizontal direction,similar micro-grooves are formed in the heat treatment in the finalbake.

Also, instead of UV irradiation in the above process, wet processing byone of an acid solution, alkali solution, quaternary ammonium saltsolution or HMDS chemicals can be used. By dipping the photo-sensitiveresin layer into such chemicals, a chemical reaction is caused on thesurface of the photo-sensitive resin layer, and the resin layer can bealtered to a substance having different thermal deformationcharacteristics.

In the present embodiment, the roughness of micro-grooves is controlledby the film thickness of the resin layer 20 and the UV irradiationenergy. FIG. 4 to FIG. 7 are micro-photographs (about X 20) of thesurface shapes of the micro-grooves which were formed by changing thefilm thickness of the photo-sensitive resin layer 20 and the UVirradiation energy. Samples of the reflection panel of themicro-photographs were prototypes fabricated by the following process.

Resist (e.g. general purpose resist LC-200 made by Shipley Co.) wasformed on the panel by a spin coating method (coated by two steps, for 3seconds at 350 rpm, and for 20 seconds at 800 rpm), the panel waspre-baked for 30 minutes at 90° C., then the entire surface of the panelwas exposed and developed to the desired film thickness (2.0 μm, 1.7 μm,1.4 μm, 1.0 μm). And after a post-bake for 40 minutes at 120° C., DUVirradiation at a desired energy (5200 mJ/cm², 3900 mJ/cm², 2600 mJ/cm²,1300 mJ/cm², 0 mJ/cm²) was performed, and a final bake for 40 minutes at200° C. was performed. Finally, aluminum was formed to be about 2000 Åas the reflection film on the resist film by a deposition method.

FIG. 4 shows micro-photographs of five samples when the film thicknessof the photo-sensitive resin layer 20 is 2.0 μm and the UV irradiationenergy is 5200 mJ/cm², 3900 mJ/cm², 2600 mJ/cm², 1300 mJ/cm² and zero.When the UV irradiation is not performed or when the irradiation energyis as low as 1300 mJ/cm², micro-grooves are not formed on the surface ofthe resin layer. However, when the irradiation energy is higher than1300 mJ/cm², micro-grooves are formed on the surface of the resin layer.In this case, the height difference and the pitch length (roughness) ofthe micro-grooves are rougher (larger height length, larger pitchlength) as the UV irradiation energy increases, and are finer (smallerheight length, smaller pitch length) as the irradiation energydecreases.

The shapes of the micro-grooves formed on the surface of the resin layer20 are random. As the photos show, in terms of shapes, at least two of agentle curved shape, a sharp angle winding shape, a closed loop shapeand a Y shaped branching shape coexist. The micro-grooves of the presentembodiment have shapes which cannot be obtained by undulation generatedby a conventional lithography processing using an artificially createdpredetermined mask pattern.

By controlling the roughness of the micro-grooves, average inclinationangles and inclination angle distribution of the undulation can beappropriately controlled.

FIG. 5 shows micro-photographs of five samples when the film thicknessof the photo-sensitive resin layer 20 is 1.7 μm and the UV irradiationenergy is 5200 mJ/cm², 3900 mJ/cm², 2600 mJ/cm², 1300 mJ/cm² and zero.Since the thickness of the resist layer is smaller than the samples inFIG. 4, the micro-grooves which are formed are finer. Micro-grooves arenot formed when the UV irradiation energy is too low, which is the sameas the samples in FIG. 4.

FIG. 6 shows micro-photographs of five samples when the film thicknessof the photo-sensitive resin layer 20 is 1.4 μm and the UV irradiationenergy is 5200 mJ/cm², 3900 mJ/cm², 2600 mJ/cm², 1300 mJ/cm² and zero.In this case, micro-grooves are even finer.

FIG. 7 shows micro-photographs of five samples when the film thicknessof the photo-sensitive resin layer 20 is 1.0 μm, and the UV irradiationenergy is 5200 mJ/cm², 3900 mJ/cm², 2600 mJ/cm², 1300 mJ/cm² and zero.In this case, the micro-grooves are even finer, but the formation ofmicro-grooves are not sufficient even with a UV irradiation energy of2600 mJ/cm².

As the above photographs of the surfaces of twenty samples clearly show,bump shapes become finer as the UV irradiation energy decreases. Alsomicro-grooves are not formed unless an irradiation energy at apredetermined reference value or more is provided. The bump shape ofmicro-grooves also depends on resist film thickness after final baking,and as the film thickness decreases, the bump shape of the micro-groovesbecomes finer.

FIG. 8 shows AFM images of three reflection panel samples. These samplesare the same as the above mentioned reflection panel samples where theUV irradiation energy is a constant 5200 mJ/cm², the resist filmthickness is 1.7 μm, 1.4 μm and 1.0 μm, and a 2000 Å aluminum reflectionfilm is formed on the resist layer.

As FIG. 8A shows, in the case of the sample where the film thickness ofthe resist film, which is the photo-sensitive resin layer, is 1.7 μm,the shape of the micro-grooves on the surface is rough, where the heightdifference of the undulation is 1.3 μm, and the average inclinationangle thereof is 13°.

As FIG. 8B shows, in the case of the sample where the film thickness ofthe resist film, which is the photo-sensitive resin layer, is 1.4 μm,the shape of the micro-grooves on the surface is somewhat finer, wherethe height difference of the undulation is 1.1 μm, and the averageinclination angle thereof is 11°.

As FIG. 8C shows, in the case of the sample where the film thickness ofthe resist film, which is the photo-sensitive resin layer, is 1.0 μm,the shape of the micro-grooves on the surface is even finer, where theheight difference of the undulation is 0.5 μm, and the averageinclination angle thereof is 8°.

As the observation result in FIG. 8 clearly shows, the averageinclination angle of the undulation changes depending on the size of theshape of the micro-grooves. In other words, as the thickness of theresist film decreases, the height difference and the average inclinationangles of the undulation decreases. Therefore, according to themanufacturing process of the present embodiment, the average inclinationangle can be controlled. The average inclination angle is an importantfactor for increasing the reflectance of the reflection panel. Thereforein terms of practicality, it is significant that the average inclinationangle can be controlled by the manufacturing process of the presentembodiment.

FIG. 9 is a graph depicting the relationship between the averageinclination angle of the reflection film and reflectance with respect tothe parallel light source and the diffuse light source. FIG. 9 showsthat the reflectance Y depends on the average inclination angle k of theundulation of the reflection film with respect to five types lightsources which light enters the reflection panel, having incident anglesto the reflection panel of 0°, 15°, 30°, 45° and an integrating spherehaving incident angel distribution of 0° to ±90° range. This dependencyis given by the later mentioned theoretical formula. The inclinationangle distribution of the undulation is a normal distribution, and theaverage inclination angle of this normal distribution is theoreticallyset.

As the theoretical values in FIG. 9 show, when the average inclinationangle exceeds 15°, the reflectance of the reflected light reflected bythe reflection film drops, since the angle of the reflected light at theboundary of the liquid crystal and the glass substrate at the frontsurface side of the reflection panel and the glass substrate exceeds thecritical angle more frequently. When the incident angle is 0° or 15°, onthe other hand, the reflectance increases as the average inclinationangle becomes lower than 5°, but a display is not often used in anenvironment where the incident angle is 0° or 15°. Therefore accordingto the theoretical values in FIG. 9, reflection films of 15° or less,preferably 8°-15° of the average inclination angle, have a relativelyhigh reflectance with respect to any incident light.

For all three samples shown in FIG. 8, the average inclination angle isin a 8°-13° range. Therefore it is clear that the average inclinationangle can be controlled in a range of high reflectance by using themanufacturing process of the present embodiment.

FIG. 10 is a graph depicting the relationship between resist filmthickness and the reflectance of the three samples in FIG. 8 when apost-bake is performed (black dots), and when post-bake is not performed(white dots). The diffused light in this case is by an integratingsphere. As described for the three samples in FIG. 8, when a post-bakeis performed, all samples with resist film thickness 1.7 μm, 1.4 μm and1.0 μm, according to the present embodiment, have high reflectancecompared to the top data of reflectance when undulation is formed by aconventional process. In other words, as the theoretical values in FIG.9 show, the samples formed to have the average inclination angle in an8°-15° range has a higher reflectance than the top data of prior art.

For the sample shown by white dots in FIG. 10, for which a post-bake wasnot performed, reflectance is lower than the conventional top data inthe area where the resist film thickness is thick, but is higher in thearea where the resist film thickness is thin. This experiment resultshows that post-bake processing is important to increase reflectance.This is probably because when a post-bake is not performed, considerablesolvent remains in the resist film after exposure and development, andthis residual solvent is degassed in the final bake process after UVirradiation, and defects are generated on the bump surface.

It is also considered that the temperature of the final bake must be sethigher than the baking temperature of alignment film formationthereafter. In other words, it is considered that completely removingthe solvent in the resist layer in the final bake process is necessaryso that the degassing phenomena does not occur in the heat treatmentthereafter, according to the result of the samples which were notsubject to post bake in FIG. 10.

FIG. 11 shows diagrams depicting the bump forms of the micro-grooves ofthe resin layer formed by the present embodiment. When the undulation isrough, as shown in FIG. 11A, the waviness of the surface of the resinlayer 20 is large, the pitch length L is long, and the height differenceH of the undulation is large. As a result, the inclination angle k tendsto be large. When the undulation is fine, as shown in FIG. 11B, thewaviness of the surface of the resin layer 20 is small, the pitch lengthL is short, and the height difference H of the undulation is small. As aresult, the inclination angle k tends to be small.

FIG. 12 shows diagrams depicting examples of the plane pattern of themicro-grooves formed by the present embodiment. As mentioned above,according to the present embodiment, the micro-grooves where the curvedpattern in FIG. 12A, the bent pattern in FIG. 12B, the looped pattern inFIG. 12C and the branched pattern in FIG. 12D are mixed, are formed onthe surface of the resin film.

FIG. 13 shows diagrams depicting examples of the UV irradiation requiredto form micro-grooves. FIG. 13A is the case when UV is irradiated on theentire surface of the resin layer 20, and in this case the shaded area,which has a predetermined depth from the surface in the depth direction,is altered by the sensitizing reaction by the UV irradiation. Thereforethe micro-grooves are formed on the surface by the heat treatment of thefinal bake thereafter, because thermal stress is caused by thedifference of the thermal deformation characteristics between thealtered layer and the unaltered layer and the stress influences thesurface.

In the case of FIG. 13B, on the other hand, the shaded area is alteredby UV irradiation using a mask on the resin layer 20. As a result, analtered layer and an unaltered layer are distributed in traversedirections. Therefore micro-grooves are formed on the surface by theheat treatment of the final bake thereafter, because thermal stress isformed by the difference of the thermal deformation characteristicsbetween the altered layer and the unaltered layer and the stressinfluences the surface. Micro-grooves are formed on the surface of theresin layer in all methods, but the process in FIG. 13A has anadvantage, because a mask is not required for the UV irradiationprocess.

The present inventors compared cases when the UV irradiation and thefinal bake of the present embodiment are performed in a conventionalbump formation process by half exposure using a mask. (1) A first samplewhere undulation is formed on the surface by half exposure, and UV isirradiated and a final bake is performed, (2) a second sample where UVis irradiated and a final bake is performed without executing halfexposure, and (3) a third sample where undulation is formed by aconventional half exposure and UV irradiation is not performed, wereprototyped, and the respective reflectances were compared.

The manufacturing process of the second sample was described abovereferring to FIG. 3. Therefore the manufacturing processes of the firstsample and the third sample will now be described. FIG. 14 showscross-sectional views depicting the manufacturing process of the firstsample. For the first sample, the above mentioned resist film 20 iscoated on the substrate 10 by spin coating, and is then pre-baked. AsFIG. 14A shows, the resist film 20 is half-exposed using a mask 42having a predetermined pattern. Half exposure is an exposure with anenergy weak enough not to sensitize all of the resist film 20 in thefilm thickness direction. Then development is performed thereafter, andthe concave parts of the pattern shape of the mask 42 are formed on thesurface of the resist film, as shown in FIG. 14B.

For the first sample, UV irradiation (e.g. 5200 mJ/cm²) of the presentembodiment is performed on the entire surface after post-baking, so thatthe surface is altered. And after the above mentioned final bake isexecuted, micro-grooves are formed on the surface of the resist film 20by the bumpy waviness corresponding to the pattern by half exposure, UVirradiation and post bake, as shown in FIG. 14C.

For the third sample, after the development process in FIG. 14B, UV isirradiated on the entire surface at an energy low enough not to formmicro-grooves (e.g. 1300 mJ/cm²). When the final bake is performedthereafter, undulation, where micro-grooves are not formed, aregenerated on the surface, as shown in FIG. 14C. By the above UVirradiation at the above mentioned low energy, only the very surface ofthe resist film 20 is altered, so that a flattening of the undulation ofthe resist film by sagging during the heating process of the final bakecan be prevented. Since the UV irradiation energy is low, micro-groovesare not formed.

FIG. 15 is a graph comparing reflectance when the diffuse light sourceof the integrating sphere is irradiated on the first, second and thirdsamples which are formed by the above process. In FIG. 15, the firstsample SM1 includes samples which are half-exposed with a plurality oftypes of pattern shapes (octagon, square, cross, pentagon, doughnut,triangle, ellipse, sector, figure eight). The second sample SM2 uses thearea which was not exposed in the half exposure. The third sample SM3also includes samples which were half-exposed with a plurality of typesof pattern shapes, the same as the first sample.

As the comparison example in FIG. 15 shows, when the present embodimentis applied with adding the half exposure process as well, a reflectancehigher than the top data of a conventional process may be obtained.However, reflectance is highest when the present invention is appliedwithout executing a half exposure, as shown in the second sample SM2. Inthe third sample SM3, where undulation is formed only by the halfexposure process, reflectance is low in all patterns. In this way theprocess of UV irradiation and final bake according to the presentembodiment, high reflectance can be implemented even if the halfexposure process and the development process using a predeterminedpattern are added.

It is preferable that the micro-grooves of the present embodiment beformed to be as random undulation as possible. According to theexperiment of the present inventors, it was observed that thick groovesor ridges are formed in a long shape at various locations when UV isirradiated on the photo-sensitive resin layer surface, and final bake isexecuted. In some cases, such undulation is not desirable as anirregular reflection function of the reflection electrodes, sincereflection directions concentrate to a certain direction, for example.So a method which can control the direction and length of themicro-grooves to some degree is desirable.

Pixel electrodes are used in the present embodiment as the reflectionelectrodes. The pixel electrodes are separately formed for each pixel,where voltage is applied independently. Here the present inventorsdiscovered that the thick grooves or ridges which formed in a long shapecan be prevented by separating the photo-sensitive resin layer intopixel units or section separation line units, and by doing somicro-grooves with more uniformity can be formed in the pixelelectrodes. The photo-sensitive resin layer may be completely separatedor be separated by forming grooves with a predetermined depth on thesurface, or may be separated by forming the resin layer such that partof the layer is thin. Pixel electrodes, however, are designed such thatcapacitance with the data line, scanning line and gate electrode come toa predetermined range, so the photo-sensitive layer must be separatedwithin a range which satisfies such conditions.

FIG. 16 shows diagrams depicting the separation of the photo-sensitiveresin layer. FIGS. 16A and 16B are plan views of the rear sidesubstrate. As FIG. 16A shows, a data line D and a scanning line S areformed on the surface of the rear face substrate, and semiconductorlayer 19 and source/drain electrodes 17 and 18 are formed at thecrossing positions. And the area partitioned by the data line D and thescanning line S become the pixel area PX. Therefore as FIG. 16B shows,the contact hole CH for connecting the source electrode 18 and the pixelelectrode 22 is formed, and the pixel electrode 22 is separatelydisposed for each pixel area.

FIG. 16C-16F show examples of separation lines for separating thephoto-sensitive resin layer. FIG. 16C is an example when the separationline 50 is formed along the scanning line S and the data line D, wherethe photo-sensitive resin layer is separated into pixel units. FIG. 16Dis an example when the separation line 50 is formed along the data lineD, where the photo-sensitive resin layer is separated into data lineunits. In FIG. 16E, the separation line 50 is formed along the data lineD, and the separation line 50 is also formed in a directionperpendicular thereto. In this case, the separation unit of thephoto-sensitive resin layer is unrelated to the pixel electrode. FIG.16F is an example when the separation line 50 is formed along thescanning line S.

FIG. 17 shows cross-sectional views depicting the process of formingseparation lines of the photo-sensitive resin layer. FIG. 17A shows astate when the gate electrodes 15, insulation film 16, semiconductorlayer 19 and drain/source electrodes 17 and 18 are formed on theinsulation substrate 10, then the photo-sensitive resin layer 20, madeof resist, is spin coated and is pre-baked. In this state, the exposureprocess for forming contact holes in the photo-sensitive resin layer 20is executed. For the exposure mask 51 at this time, a mask pattern,where the area 53, corresponding to the contact hole, completelytransmits light, the area 55 corresponding to the separation linepartially transmits light, and the other area 54 shields lightcompletely, is formed on the transparent substrate 52. For example, thearea 54 is formed by a light shielding film made of chromium, and thearea 55 can be formed by a half exposure film comprised of molybdenumsilicide. If exposure using such an exposure mask is executed, theposition of the contact hole of the photo-sensitive resin layer 20 iscompletely exposed, and the area corresponding to the separation line ishalf-exposed.

When the development process is performed thereafter, contact holes CHwhich penetrate the resin layer are formed on the photo-sensitive layer20 at positions corresponding to the source electrodes 18, and groovesas separation lines 50, having a predetermined depth, are formed on thesurface of the resin layer, as shown in FIG. 17B. Contact holes CH areformed only in narrow areas, and do not have the function of separatingthe resin layer 20. The separation line 50, however, separates at leastthe surface of the resin layer 20, so long extended grooves and ridges,generated in the micro-grooves formed by the UV irradiation and finalbaking processes, can be prevented.

In FIG. 17A, a special exposure mask 51 was used. However the patterningof the resin layer shown in FIG. 17B is also possible by executingnormal exposure using a mask to form contact holes, and executinghalf-exposure using another mask to form a separation line. It is alsopossible to execute normal exposure using a mask to form a separationline so that the resin layer 20 is completely separated by theseparation line 50.

The separation line 50 need not be formed on the front face side of theresin layer 20. The separation line 50 can be formed on the rear faceside, for example. In that case, the data line D, formed on theinsulation layer 16, may have the function of the separation line 50.This is because the thickness of the resin layer 20 becomes partiallythinner at the part where the data line D exists. By this, the formationof micro-grooves is cut off, and the generation of long extended groovesand ridges can be prevented.

As FIG. 17B shows, it is desirable that the separation line 50 is formedin the separated area of the pixel electrodes 22 (indicated by thebroken line in FIG. 17B) which are formed on the resin layer 20. Becauseof this, influence on parasitic capacitance between the pixel electrodes22, and the gate electrodes 15 or other electrodes, can be minimized.

FIG. 18 shows micro-photographs of micro-grooves when a separation lineis formed and when not formed. In these examples, a separation line isformed and is not formed on the reflector, which is the same with thesamples in FIG. 6 to FIG. 9. FIG. 18A is an example of micro-grooveswhen a separation line is formed, and FIG. 18B is an example ofmicro-grooves when a separation line is not formed.

As these micro-photographs show, in the case of example FIG. 18B, wherea separation line is not formed, long extended grooves or ridgespartially exist, but in the case of example FIG. 18A, where a separationline is formed, such extended grooves or ridges do not exist, and themicro-grooves are more uniform.

For samples of the above embodiment, a general purpose resist, LP200made by Shipley Co., was used for the photo-sensitive resin layer. Itwas confirmed that similar micro-grooves are also formed when AFP 750resist, made by Clariant Japan, instead of the above mentionedphoto-sensitive resin, was used.

As described above, according to the present embodiment, micro-grooveswith random undulation can be formed on the surface of thephoto-sensitive resin layer by a simple process of forming partiallyaltered areas of the photo-sensitive resin layer by UV irradiation, andperforming heat treatment thereafter. Also the shape and the directionof the micro-grooves can be controlled relatively easily by variousprocess conditions. Therefore a reflection function, effective for areflection liquid crystal display device, can be implemented by forminga reflection layer on a resin layer which has such micro-grooves. Byusing pixel electrodes for the reflection layer, an even simplerreflection liquid crystal display device can be implemented.

[Modified Process of Micro-Grooves 1]

The main point of the present embodiment is to adjust the distributionof the thermal deformation characteristics of photo-sensitive resin whenforming micro-grooves, so as to control the shape of the undulation ofthe photo-sensitive resin as desired.

Specifically, the preferred methods are a method of adjusting theirradiation energy to be exposed on the photo-sensitive resin, a methodof using an arbitrary mask pattern at this time, a method of setting atleast one of the number, shape and arrangement of the composing elementsprovided on a TFT substrate to a desired value using the composingelements (e.g. gate electrode, CF electrode, pixel electrode, contacthole) when at least one of the composing elements is formed, and amethod of forming an undulation pattern on the substrate by selectivelyetching the surface of the substrate, and, using these methods, thedistribution of the thermal deformation characteristics of the resinlayer is adjusted, and the undulation shape of the resin layer iscontrolled.

Here an example of a method of adjusting the irradiation energy when thephoto-sensitive resin is exposed will be shown first. FIG. 57 shows aconventional manufacturing process and the manufacturing process of thepresent invention of the undulation or bump formation methodrespectively.

In a conventional formation process as shown at left hand side of FIG.57, resist 123, which is resin for protrusion formation, is coated onthe TFT substrate 122 where TFT element 121 is formed, then theprotrusions 124 are formed by photo-lithography, as shown in FIG. 57A to57E. Then the average inclination angles of the undulation 125 areoptimized by forming flattening resin 125, the contact hole CH is formedby photo-lithography, and the reflection electrode 126 comprised of Alis formed. In this way, a resin formation process and photo-lithographyare conventionally required twice respectively, as shown in FIG. 58A.

According to the present invention, on the other hand, thephoto-sensitive resin 123, such as resist, is coated, the contact holeCH is formed by a photo-lithography process, and a post-bake isperformed at a temperature of less than 160° C., as shown in FIG. 57F to57H. Then the thermal deformation characteristics of the photo-sensitiveresin 123 are distributed by irradiating UV light (preferably DUV (deepUV)) with an irradiation higher than normal exposure conditions, to forma contact hole CH, then undulation (micro-grooves) 128 like wrinkles areformed at the surface of the photo-sensitive resin 123 by performingheat treatment equal to or higher than the post-bake temperature. Theprocess up to this point is the same as the process in FIG. 3. Then thereflection electrode 126 comprised of Al is formed.

In this way, according to the present embodiment, it is sufficient toperform the resin formation process and photo-lithography only oncerespectively, as shown in FIG. 58B, so the manufacturing process can beconsiderably simplified and a photo mask for bump formation is notnecessary. Also, by controlling the process conditions, including theresin film thickness, bake conditions, and UV curing conditions, theaverage inclination angles of the micro-grooves can be controlled.Therefore it is possible to implement a reflection liquid crystaldisplay device having higher reflection characteristics than prior art.The reflectance characteristics are shown in FIGS. 9, 10 and 15.

CONCRETE FABRICATION EXAMPLES Fabrication Example 1

A reflection panel prototype was fabricated under the followingfabrication conditions.

Photo-sensitive resin: LC-200 (general purpose resist made by ShipleyCo.)

Using a spinner, the above mentioned photo-sensitive resin material wasrotated for 3 seconds at 350 rpm, then rotated for 20 seconds at 800 rpmto form the resin layer.

Pre-bake: 30 minutes at 90° C.

Film thickness was changed by exposing the entire surface of the panel.

Post bake: 40 minutes at 120° C.

UV curing: Using a UV irradiation device made by ORC, UV was irradiatedon the entire surface of the resin layer at 5200 mJ/cm² (measured by aUV25 sensor made by ORC).

Resist final bake: 40 minutes at 200° C.

Reflection material: Al with a 200 nm film thickness (deposited byresistance heating)

A liquid crystal panel was fabricated using a reflection electrodefabricated under the above mentioned conditions, and reflectioncharacteristics were evaluated using an integrating sphere. As a result,as FIG. 9 shows, it was determined that a reflection liquid crystalpanel with better reflection characteristics than prior art wasimplemented.

Fabrication Example 2

Fabrication example 2 can be applied to the case when pattern exposureis executed.

The following fabrication conditions are when the photo-sensitive resinis half-exposed and the pattern sags by heat, in order to form areflection electrode having the desired reflection characteristics. Whenthis system is applied to a TFT substrate, exposure is required twice,but resin formation can be only once. However, the problem is thatreflection characteristics greatly depend on the exposure conditions andheat sagging conditions. To alleviate this problem, we invented a methodof adding a micro-groove formation process to the half exposure process.The fabrication conditions are as follows.

Photo-sensitive resin: LC-200 (general purpose resist made by ShipleyCo.)

3 seconds at 350 rpm first, then 20 seconds at 800 rpm using a spinner.

Pre-bake: 30 minutes at 90° C.

Using photo-masks (having an octagon, square, cross, pentagon, doughnut,triangle, ellipse, sector, figure eight shapes, and an area without apattern. Here the area without a pattern is an area where onlymicro-grooves are formed), contact exposure was executed (under the sameexposure conditions) using a large exposure system.

Development process: 50 seconds

Post-bake: 40 minutes at 120° C.

UV curing: 5200 mJ/cm² (micro-groove forming conditions)

UV curing: 1300 mJ/cm² (micro-groove non-forming conditions, preventssagging by heat), optimized under half exposure conditions

Resist final bake: 40 minutes at 200° C.

Reflection material: Al at a 200 nm film thickness (deposited byresistance heating)

A liquid crystal panel was fabricated using a reflection electrodeformed under the above mentioned conditions, and the reflectioncharacteristics were evaluated using an integrating sphere. As a result,as FIG. 15 shows, it was determined that a reflection panel havingstable and high reflection characteristics can be fabricated by addingmicro-groove formation conditions to the half exposure system. However,only the area where only micro-grooves are formed on the part with nopattern formation showed the highest reflection characteristics.

Fabrication Example 3

In fabrication example 3, it was discovered that when micro-grooves areformed on a flat substrate, uniformity from a macro-view improves if thesurface of the resin is separated into blocks by half exposure, comparedwith the case of not separating into blocks, as shown in FIG. 18.

FIG. 59 shows micro-photographs depicting an example of micro-grooveformation when block separation was performed by half exposure.

As FIG. 59 shows, wrinkles of micro-grooves are confined to a block. Inother words, it is known that micro-grooves can be separated by halfexposure. It was also discovered that the shape of micro-grooves can becontrolled by block shape and depth of separation (exposure conditions).

Fabrication Example 4

In the block separation shown in fabrication example 3, it wasdiscovered that it is not necessary to form block separation on thesurface of the resin layer by half exposure, but that micro-grooves canbe separated or that shape thereof can be controlled by creating filmthickness distribution on the photo-sensitive resin by formingundulation on the substrate surface. In other words, film thicknessdistribution is created on the photo-sensitive resin layer by a data busline, gate line and auxiliary electrode Cs line on the substrate shownin FIGS. 16 and 17, by which blocks of micro-grooves are separated.

FIG. 60 is a micro-photograph showing the micro-grooves formed infabrication example 4.

Here, AFP 750 (made by Clariant Japan) is coated on a TFT substrate,pre-bake is performed, a contact hole is exposed using a stepper, theresist is developed, and post-bake is performed for 80 minutes at 135°C., then UV is irradiated at 2600 mJ/cm² for UV curing, and final bakeis performed on the resist at 200° C. for 60 minutes, to form themicro-grooves.

As FIG. 60 shows, micro-grooves are separated on the data bus, gate lineand Cs line, which are the composing elements on the substrate. This isbecause resist film thickness decreases on the data bus, gate line andCs line, and micro-grooves are separated.

FIG. 61 is a micro-photograph of one polarizer type TFT drivenreflection liquid crystal device fabricated using a TFT substrate and CFsubstrate, where an Al electrode is formed by sputtering and a pixelelectrode is formed by separation by photo-lithography.

As FIG. 61 shows, micro-grooves are deformed not only on the data bus,gate line and Cs line but also near the contact hole. This indicatesthat bump shapes on the reflection electrode surface can be controlledby the size, shape, arrangement and number of contact holes.

Table 1 shows the characteristics comparison between an actuallyfabricated reflection panel and reflection panels made by othercompanies.

As Table 1 shows, the fabricated reflection panel exhibits higherreflection characteristics than other companies, both in the 30°incident system using a point light source and in measurement by anintegrating sphere using a diffuse light source.

TABLE 1 Reflectance comparison with reflection LCDs made by othercompanies (reflector of a 100% white display) Measurement Present systemCompany A Company B Invention 30° incident 18 18 35 Integrating 11 14 16sphere

The 30° incidence indicates reflectance (standard white panel: 100%) atthe front face of the panel under a 30° incident point light source, andthe integrating sphere indicates reflectance (standard white panel:100%) at the front face of the panel under a uniform diffuse lightsource with full attachment.

Fabrication Example 5

The shape of the micro-grooves can be controlled by controlling thearrangement and shape of the electrode layer and the inter-layerinsulation film layer of the gate electrode, Cs electrode (same layer asthe gate electrode) and the data electrode, which are the composingelements of a TFT substrate.

FIG. 62 shows plan views depicting examples of the TFT substrate. FIG.62A shows a normal TFT substrate where a gate electrode 131, Cselectrode 132, data electrode 133 and TFT element 134 are formed. FIG.62B is an example when two lines of linear structures 136 are formed ina diagonal direction during patterning of the gate electrode 131 and Cselectrode 132, in addition to the normal TFT structure. FIG. 62C is anexample when n number of circular structures 137 are formed in the sameway as FIG. 62B, FIG. 62D is an example when two lines of linearstructures 136 are formed in parallel with the data electrode 133, FIG.62E is an example when two circular structures 137 are formed just likeFIG. 62C, FIG. 62F is an example when n number of linear structures 136are formed in parallel with the data electrode 133, and n number oflinear structures 136 are formed in parallel with the gate electrode133, and FIG. 62G is an example when four linear structures 136 areformed in the diagonal direction. The photo-sensitive resin layer isformed on the structure shown in the above mentioned plan views, andmicro-grooves are formed on the surface.

As illustrated, wrinkle shapes of the micro-grooves generated on thesurface of the photo-sensitive resin can be controlled by formingstructures using these materials so as to create step differences in thepixel area when each constituting element of the gate electrode 131, Cselectrode 132 (the same layer as the gate electrode 131) and dataelectrode 133 are formed. In this case, the structures are patterned atthe same time with each constituting element, so the number ofprocessing steps are unchanged. Because of this, it is possible to adddirectivity to the reflection characteristics and to control alignmentof the liquid crystal layer by the micro-groove azimuth.

Fabrication Example 6

Micro-grooves can be controlled in the same way by forming the stepdifference shape of fabrication example 5 by selectively etching the TFTstructure.

Fabrication Example 7

Bump shapes at the surface of the reflection electrode can be controlledby the size, shape, arrangement and number of contact holes forelectrically connecting the drain electrode (the same layer as the dataelectrode) of the TFT substrate and the reflection electrode. In otherwords, by forming a plurality of contact holes to be a predeterminedshape in a pixel, undulation can be formed on the photo-sensitive resinlayer and the wrinkle shape of the micro-grooves formed on the surfacecan be controlled.

FIG. 63 shows examples. FIG. 63A shows a plan view of a normal TFTsubstrate where the gate electrode 131, Cs electrode 132, data electrode133, TFT element 134 and contact hole 138 are formed. FIGS. 63B, 63E,63F are examples when the number of contact holes 138 are changed, andFIGS. 63C, 63D, 63G and 63H are examples when the shape of the contactholes 138 are changed. In these examples, the source electrode 18 shownin FIG. 2 is formed on the entire face of a pixel block, and a pluralityof contact holes CH are formed thereon. The wrinkle shapes of themicro-grooves are formed with contacts hole CH as the center.

As FIG. 63 shows, the micro-grooves generated on the surface of thephoto-sensitive resin can be controlled by controlling the size, shape,arrangement and number of the contact holes 138.

Fabrication Example 8

It has been confirmed that the liquid crystal aligns along the groove onthe surface of the reflection electrode where the micro-grooves of thepresent invention are formed, and by using this characteristic, a randomalignment type reflection liquid crystal display device can beimplemented without performing special alignment processing, such asrubbing processing on the alignment film, in the horizontal alignment,vertical alignment and hybrid alignment (HAN), and the panel formationprocess can be simplified.

As described above, according to the present embodiment, processsimplification, yield improvement, and a decrease in manufacturing costcan be implemented, a reflection electrode which can stably implementhigh reflection characteristics can be formed, and a reflection liquidcrystal display device with high reliability whereby a high brightnessdisplay is possible can be implemented.

[Modified Process of Micro-Groove 2]

A rough configuration of the reflection liquid crystal display device ofthe present embodiment is the same as the configuration shown in FIG. 2.

The main point of the present embodiment is that when undulation isformed on the surface of the resin layer by performing heat treatment onthe resin layer, a part which thermal deformation characteristics aredifferent from the resin is created in the resin layer, or a materialwhich thermal deformation characteristics are different from the resinis mixed into the resin layer, so as to control the bump shape of themicro-grooves to be a desired shape.

Specifically, suitable methods include a method of dispersing particleswhich have different thermal deformation characteristics into the resinlayer, a method of forming the above mentioned part by layering anotherresin layer having different thermal deformation characteristics in theresin layer, a method of forming the above mentioned part by forminganother resin layer having different thermal deformation characteristicsin the resin layer into a predetermined shape using a pattern, and amethod of forming the part having different thermal deformationcharacteristics by performing partial processing (e.g. irradiatingenergy rays selectively onto the resin layer or changing the irradiationintensity of the energy ray). The bump shape of the resin layer iscontrolled such that the ridge line shape becomes at least one of aline, curve, loop and branch shape.

CONCRETE FABRICATION EXAMPLES Fabrication Example 1

As FIG. 64 shows, novolak photo-sensitive resin 102, where SiO₂particles 103 with about a 1 μm diameter are dispersed, is coated on theglass substrate 101, a post bake is performed at 160° C., then UV isirradiated at an irradiation energy equal to or higher than imageexposure condition, so as to form an area with different thermaldeformation characteristics in the photo-sensitive resin 102. Then heattreatment is performed a temperature equal to or higher than a post baketemperature, so as to form fine wrinkled undulation 104 on the surfaceof the photo-sensitive resin 102 with the particles 103 having differentthermal deformation characteristics as cores. And a reflection layer(not illustrated) such as Al is formed on the photo-sensitive resin 102,so as to fabricate a reflector having a surface which reflects the shapeof the undulation 104.

In this example, silicon dioxide particles having different thermaldeformation characteristics are dispersed in the photo-sensitive resinlayer, and a distribution having different thermal deformationcharacteristics is formed in the photo-sensitive resin layer by UVexposure. It was discovered that finer wrinkle shapes are formed afterheat treatment is performed compared with the case when silicon dioxideparticles were not dispersed.

Fabrication Example 2

As FIG. 65 shows, a layer 105 having thermal deformation characteristicsdifferent from the photo-sensitive resin 102 is layered in thephoto-sensitive resin 102. After post baking at 160° C., UV isirradiated at irradiation energy equal to or higher than image exposureconditions, so as to form an area having different thermal deformationcharacteristics in the photo-sensitive resin 102. Then heat treatment isexecuted at a post bake temperature or higher. As a result, finerwrinkle undulation 104 is formed on the surface of the photo-sensitiveresin 102 because the thermal deformation characteristics of each layerare different. Then the reflection layer (not illustrated) such as Al isformed on the photo-sensitive resin 102, so as to fabricate a reflectorhaving a surface which reflects the shape of the undulation 104.

Fabrication Example 3

As FIG. 66 shows, a resin 106 having thermal deformation characteristicsdifferent from the photo-sensitive resin 102 is formed on the substrate101 by patterning, and is covered by the photo-sensitive resin layer102. To prevent diffraction, the pattern shapes are preferred to berandom. After post-bake is executed at 160° C., UV is irradiated at anirradiation energy equal to or higher than the image exposureconditions, so as to form an area having different thermal deformationcharacteristics from the photo-sensitive resin 102 in thephoto-sensitive resin 102. Then heat treatment is performed at apost-bake temperature or higher, and as a result, finer wrinkledundulation 104 are formed on the surface of the photo-sensitive resin102, because the thermal deformation characteristics of each layer aredifferent. Then a reflection layer (not illustrated), such as Al, isformed on the photo-sensitive resin 102, so as to fabricate a reflectorhaving a surface which reflects the shape of the undulation 104.

Fabrication Example 4

As FIG. 67 shows, UV is selectively irradiated on the photo-sensitiveresin, so as to form an area 107 having different thermal deformationcharacteristics. After post baking at 160° C., UV is irradiated on theentire surface at a irradiation energy equal to or higher than the imageexposure conditions, so as to form an area having different thermaldeformation characteristics in the photo-sensitive resin 102. Then heattreatment is performed at a post bake temperature or higher, and as aresult, finer wrinkled undulation 104 are formed on the surface of thephoto-sensitive resin 102, because the thermal deformationcharacteristics of each layer are different. Then a reflection layer(not illustrated), such as Al, is formed on the photo-sensitive resin102, so as to fabricate a reflector having a surface which reflects theshape of the undulation 104.

As described above, according to the present embodiment, the roughnessof the display screen is controlled by meticulously controlling thewrinkled undulation on the surface of the photo-sensitive resin, and asimplification of process, improvement of yield and decrease inmanufacturing cost can be implemented, and a reflection type liquidcrystal display device with high reliability, which can display withhigh lightness, can be implemented by forming a reflection electrodewhich can stably implement high reflection characteristics.

In the above example, the process of irradiating UV on the entiresurface can be omitted if material having different thermal deformationcharacteristics is mixed, layered or distributed in the photo-sensitiveresin layer.

[Modified Process of Micro-Groove 3]

A rough configuration of the reflection liquid crystal display device ofthe present embodiment is the same as the configuration shown in FIG. 2.

The main point of the present embodiment is that when thermalcharacteristics distribution is created in the resin layer, thedistribution of the shrinkage factor or the expansion factor is createdin the thickness direction of the resin layer by irradiating the lightwith a predetermined exposure energy on the surface of the resin layer,so as to control the bump shape of the resin layer. Specifically, it ispreferable to set the exposure energy to be 1000 mJ/cm² or higher value.

CONCRETE FABRICATION EXAMPLES Fabrication Example 1

Resist having a different shrinkage factor is layered on the glasssubstrate 201 as a resin layer, and is baked at 200° C. for 60 minutes,then it was examined how undulation (micro-grooves) are generated on theresist surface. Examination showed that undulation (micro-grooves) weregenerated on the surface when the layer 203, having a small shrinkagefactor, is formed on a layer 202 having a large shrinkage factor, asshown in FIG. 68, but the undulation (micro-grooves) were not generatedwhen the layer 202, having a large shrinkage factor, is formed on thelayer 203 having a small shrinkage factor.

The reason follows. As FIG. 69 shows, stress generated in the layer 202with a large shrinkage factor at the bottom layer influences the layer203 with a small shrinkage factor at the top layer, and deformation isgenerated in the layer 203 with a small shrinkage factor at the toplayer. If the layer 203 with a small shrinkage factor is at the bottom,little stress is generated, and the top layer 202 with a large shrinkagefactor is not influenced, so deformation by heat treatment is notgenerated and micro-grooves are not formed.

Therefore when two types of photo-sensitive resin layers with differentthermal shrinkage factors are layered, it is necessary to form a resistwith a high thermal shrinkage factor at the bottom layer and a resistwith a low thermal shrinkage factor at the top layer.

Fabrication Example 2

4000 mJ/cm² of UV is irradiated on the novolak photo-resist coated onthe glass substrate to cause a cross-link reaction of resist near thesurface. The novolak resin near the surface of the resist polymerizes byan oxidation reaction, as shown in FIG. 70 (FIG. 70 is one example ofthe reaction). Since the polymerized novolak has a smaller shrinkagefactor than the non-polymerized novolak, distribution of the shrinkagefactors can be formed such that the shrinkage factor is small at theresist surface and the shrinkage factor is large inside the resist.

Therefore by forming a novolak photo-resist layer on the glass substrateand irradiating UV on the entire surface to cross-link the resist at thesurface, a structure where the top layer has a small shrinkage factorand the bottom layer has a large shrinkage factor can be created.Micro-grooves can be formed by performing heat treatment at the surfacethereafter.

Fabrication Example 3

Resist AFP 750 (made by Clariant Japan) is coated on the 0.7 mm thickglass substrate to a 3 μm thickness, and solvent in the resist isevaporated by baking the resist for 30 minutes at 90° C. in a cleanoven. UV is then irradiated at 0-6500 mJ/cm². After irradiating UV, theresist was baked for 60 minutes at 200° C. in a clean oven, and theresult of observing the shape of the resist by microscope is shown inFIG. 71.

As FIG. 71 shows, undulation (micro-grooves) are generated on the resistsurface by irradiating UV at a 2600 mJ/cm² or higher energy.

We examined how undulation is generated on the resist surface bychanging the baking temperature (time is fixed to 30 minutes) before UVirradiation and dose of UV. This result is shown in FIG. 72. The blackdot indicates a case when micro-grooves were generated, and X indicatesa case when micro-grooves were not generated.

As FIG. 72 shows, undulation is generated under specific conditions,that is, when the bake temperature before UV irradiation is 135° C. orless and the dose of UV is 1000 mJ/cm² or more.

FIG. 73 shows the result of examining the state of the generation ofundulation when the bake temperature is changed before UV irradiationand after UV irradiation while fixing the dose of UV at 3900 mJ/cm².

The result shows that undulation is generated when the bake temperaturebefore UV irradiation is 135° C. or less and the bake temperature afterUV irradiation is higher than that before UV irradiation. However, ifthe bake temperature before UV irradiation is set to 90° C. or less,bubbles are generated, as the micro-photograph in FIG. 74 shows. This isbecause the solvent in the resist is not completely evaporated.

Table 2 shows the results when the bake temperature before UVirradiation and bubble generation are examined. As Table 2 shows,bubbles are not generated if the bake temperature before UV irradiationis 90° C. or more. Therefore it became clear that uniform undulation(micro-grooves) without defects, due to bubble generation, can be formedby baking in a 90-135° C. temperature range. If the temperature exceeds150° C., it is a glass transition temperature or higher wheremicro-grooves are not formed.

TABLE 2 Bake temperature and bubble generation states before UVirradiation Temperature Bubble generation Remarks  25° C. Generated  30°C. Generated  50° C. Generated  70° C. Generated  80° C. Generated  90°C. No 105° C. No 120° C. No 135° C. No 150° C. No No undulationgenerated

Fabrication Example 4

Undulation were examined when the resist film thickness is changed.Resist AFP 750 (30 cP viscosity) is coated on the glass substrate whilechanging the rotation frequency in an 800-5000 rpm range, and is bakedfor 30 minutes at 90° C. After baking, UV is irradiated at 3900 mJ/cm²,and baking is finally performed for one hour at 200° C.

FIG. 75 shows micro-photographs of undulation (micro-grooves) fabricatedas above.

As FIG. 75 shows, the amplitude and cycle of the undulation decreases asthe rotation frequency of the spinner increases (as the film thicknessof the resist decreases). Even in the case of using resist AFP 750changing between 40 CP and 15 CP viscosity, we observed a phenomenawhere film thickness decreased along with a decrease in the amplitudeand cycle of undulation.

A reflector was fabricated by depositing aluminum (Al) on the undulationformed at the resist surface to be a 200 nm film thickness. Thereflector and 0.7 mm thick glass substrate were optically contacted withimmersion oil (1.53 refraction index), and reflection characteristicswere measured using an integrating sphere. Since the refraction index ofthe liquid crystal and the glass substrate are both about 1.5, areflection type liquid crystal display device can be created virtuallyby optically contacting the glass substrate on the reflector.

FIG. 76 shows the result of measuring the reflectance.

The abscissa in FIG. 76 is the resist film thickness which was measuredusing a non-contact three-dimensional shape measurement device (made byHishiko). As FIG. 76 shows, a 60% or higher reflectance is obtained forresist film thickness in a 1.5-4 μm range. Since reflectance on anewspaper surface is about 60%, a bright reflection liquid crystaldisplay device can be implemented by setting the resist film thicknessto 1.5-4 μm. A resist with a different viscosity CD was used to changethe resist film thickness.

Fabrication Example 5

Using resists LC-200 and S1808 (both made by Shipley) the generation ofundulation was examined, and a result similar to the result of thefabrication example 1 was obtained. In the case of LC-200, S1808 and AFP750, fine undulation was generated even if the structure of novolakresin in the resist is different, so it was confirmed that undulationcan be implemented if the resist is a novolak resin type.

We performed a similar experiment using AFP 750 without a sensitizingagent, and undulation was generated even with a resist without asensitizing agent. By this, it was confirmed that undulation isgenerated by a novolak resin and a sensitizing agent in the resist isnot necessary for generating undulation.

Fabrication Example 6

Resist AFP 750 is coated on a 0.7 mm thick glass substrate at a 3 μmthickness, baked for 30 minutes at 90° C. in a clean oven, then UV wasirradiated at 3900 mJ/cm². After UV irradiation, undulation wasfabricated by baking the resist for 60 minutes at 200° C. in a cleanoven. A reflector was formed by forming a 300 nm aluminum film on theundulation. Using this fabricated reflector and a glass substrate with atransparent electrode ITO, the liquid crystal cell shown in FIG. 77 wasfabricated using a 4 μm diameter spacer.

For the liquid crystal, FT-5045 made by Chisso was used, and, as shownin FIG. 77, a polarizer and ¼ wavelength plate were glued onto the frontface of the 0.7 mm thick glass substrate. As a result of observing thisliquid crystal cell indoors, it was clear that a good light display wasobtained.

When voltage was applied, it was confirmed that a dark state wasobtained and the contrast of the light state and dark state is large.FIG. 78 shows the result of measuring reflectance when the appliedvoltage is changed using an integrated sphere. In FIG. 78, the abscissais the applied voltage to the cell, and the white display changes to ablack display by changing this applied voltage to the cell. As FIG. 78shows, it was confirmed that a good display with high reflectance (30%)and high contrast (18) was obtained.

Fabrication Example 7

Resist AFP 750 is coated on a 0.7 mm thick glass substrate to be a 3 μmthickness, baked for 30 minutes at 90° C., and UV was irradiated at 32mJ/cm² using a mask where circular patterns with a 10 μm diameter arearranged at random. After UV irradiation, the resist film was soaked inMF 319 developer so as to form circular patterns. After baking thesubstrate for 40 minutes at 120° C. to completely evaporate thedeveloper in the resist, UV was irradiated at 1300 mJ/cm² and 2600mJ/cm². Then the resist was baked for one hour at 200° C. so as to formundulation.

FIG. 79 shows a micro-photograph of a patterned resist substrate afterbaking. As the photograph shows, fine wrinkled undulation is generatedon the circular patterns by UV irradiation. However it was discoveredthat fine undulation is not generated when the same experiment wasperformed by increasing the UV dose to 80 mJ/cm² to form circularpatterns.

So we examined the UV dose and the micro-pattern generation statusduring patterning. Table 3 shows the result, and FIG. 80 showsmicro-photographs of substrates when 80 mJ/cm² and 35 mJ/cm² areirradiated respectively.

As Table 3 shows, if the first patterning is executed at 60 mJ/cm² orless exposure energy, fine wrinkle shapes are generated to be patternedundulation. This means that if the exposure energy of half exposureduring patterning is too high, the undulation formed thereby becomedeep, and micro-grooves are not easily formed on the surface. Thereforemicro-grooves are effectively formed on the surface by forming shallowundulation with a relatively low exposure energy.

TABLE 3 Relationship between UV dose and micro-undulation(micro-grooves) generation during patterning UV dose Generation of(mJ/cm²) micro-undulation 10 Generated 20 Generated 30 Generated 35Generated 40 Generated 45 Generated 50 Generated 60 Generated 70 Notgenerated 80 Not generated 100 Not generated

Fabrication Example 8

As FIG. 81 shows, striped undulation 303 (height: 0.5 μm, width: 15 μm)were formed on the glass substrate 301, and resist layer 304 (AFP 750)was coated thereon. After baking for 30 minutes at 90° C., UV at 3900mJ/cm² was irradiated, and the resist was baked for one hour at 200° C.

FIG. 82 shows micro-photographs of fine micro-groove shapes which aregenerated after baking.

For comparison, FIG. 82 also shows a micro-photograph of a finemicro-groove shape when undulation is not formed under the resist film.When undulation exist under the resist film, a step difference is formedon the surface of the resist, where the stress applied inside the resistdiffers, so the fine micro-groove shape becomes different from theperipheral area.

As described above, according to the present embodiment, asimplification of process, improvement of yield and a decrease inmanufacturing cost can be implemented, and a reflection liquid crystaldisplay device with high reliability which can display with highlightness can be implemented by forming a reflection electrode which canstably implement high reflection characteristics.

[Control of Inclination Angle Distribution of Reflector]

FIG. 19 is a diagram depicting an actual environment where thereflection type liquid crystal display device based on the presentembodiment is used. In the environment where the reflection type liquidcrystal display device is used, light sources exist in variouslocations. Therefore, considering various environments of use, as shownin FIG. 19, it is necessary to assume the case when the reflection typeliquid crystal display device is positioned under a uniform diffuselight source placed inside a sphere. Under such a use environment, allincident lights that exist in the solid angle of the half sphere areirradiated into the display panel.

To determine the light intensity L to enter the reflection type liquidcrystal display device, X-Y-Z axis, incident angle θ_(i) and azimuthangle φ_(i) are defined as shown in FIG. 20. The incident angle θ_(i) isan angle between the Z axis and incident light, and azimuth angle φ_(i)is an angle between the incident light and the X axis. If the lightintensity per unit area of the sphere shown in FIG. 19 (hereafterintegrating sphere) is I (θ_(i), φ_(i)), then the light intensity dL isgiven by

$\begin{matrix}{{dL} = {{I\left( {\theta_{i},\varphi_{i}} \right)} \cdot {dw}}} \\{= {{{I\left( {\theta_{i},\varphi_{i}} \right)} \cdot {ds}}\text{/}r^{2}}}\end{matrix}$

Here, ω is a solid angle, ds is a unit area on the spherical surface ofthe integrating sphere, and r is a radius of the integrating sphere, andif the integrating sphere is a uniform diffuse light, then the abovementioned light intensity I becomes a constant.

Also, the incident light is irradiated onto the display panel from adiagonal direction with incident angle θ_(i), so the light intensityirradiated on the display panel is attenuated for sin θ_(i).

dL=I(θ_(i), φ_(i))·sin θ_(i) ·ds/r ²  (1)

As shown in FIG. 20, the unit area ds is given by

ds=(r·sin θ_(i) ·dφ _(i))·r·dφ _(i)  (2)

Therefore, if the formula (2) is substituted for formula (1), and thelight intensity dL is integrated in the range of incident angle θ_(i),0−π/2, and azimuth angle φ_(i), 0−2π, then the incident light intensityL of the display panel is given as follows.

$\begin{matrix}{{L = {\int_{0}^{\theta_{i} = \frac{\pi}{2}}{\int_{0}^{\varphi_{i} = {2\; \pi}}{{I\left( {\theta_{i},\varphi_{i}} \right)}\sin \; \theta_{i}\cos \; \theta_{i}\ {\theta_{i}}}}}}\ } & (3)\end{matrix}$

Therefore the light intensity f (θ_(i)), which enters from the polarθ_(i) direction, is given by the function in the integration in formula(3), and is given as follows.

f(θ_(i))=I(θ_(i), φ_(I)) sin θ_(i) cos θ_(i)  (4)

Sin θ_(i) in the formula (4) results from the area of the diffuse lightsource of the integrating sphere for each unit incident angle θ_(i), andthis means that the light source area of the incident light from justabove the display panel (incident angle θ_(i)=0) is small (sin θ_(i)=0),and the light source area of the incident light from the lateraldirection of the display panel (incident angle θ_(i)=π/2) is wide (sinθ_(i)=1). The cos θ_(i) in the formula (4) is an attenuation componentdue to the incident angle, and this means that the attenuation of theincident light from just above the display panel (incident angleθ_(i)=0) is very little (cos θ_(i)=1), and the attenuation of theincident light from the lateral direction of the display panel (incidentangle θ_(i)=π/2) is large ((cos θ_(i)=0).

FIG. 21 is a diagram depicting the case when light enters the reflectiontype display device and is reflected.

In the case of the reflection type liquid crystal device shown in FIG.2, the refractive index n of the glass substrate at the display side andthe liquid crystal layer are roughly 1.5, so as FIG. 21 shows, in thestructure it is assumed that the reflector 60 comprising a substratehaving the reflection electrode shown in FIG. 21 is covered with themedium 61 with the refractive index n comprised of a liquid crystallayer and a substrate at the display side, which are formed thereon.Then the incident light which enters the air layer at incident angleθ_(i) has incident angle θ_(i)′, in the medium 61, is reflected by thereflector 60 at the reflection angle θ_(o)′ in the medium 61, and isemitted to the air layer at the reflection angle θ_(o).

When the light enters from the air layer to the medium 61, a part of thelight becomes reflected light R, and does not enter into the medium, soconsidering this, the intensity f (θ_(i)′) of the light which enters thereflector 61 at the incident angle θ_(i)′ can be given as follows.

$\begin{matrix}\begin{matrix}{{f\left( \theta_{i}^{\prime} \right)} = {\left\lbrack {1 - {R\left( \theta_{i} \right)}} \right\rbrack \cdot {f\left( \theta_{i} \right)}}} \\{= {{\left\lbrack {1 - {R\left( \theta_{i} \right)}} \right\rbrack \cdot {I\left( {\theta_{i},\varphi_{i}} \right)}}\sin \; \theta_{i}\cos \; \theta_{i}}}\end{matrix} & (5)\end{matrix}$

Here, R (θ_(i)) is the reflectance of the light which reflects at theinterface of the above mentioned air layer and the medium 61 with therefractive index n. And the following relationship is establishedbetween the incident angle θ_(i) in the air layer and the incident angleθ_(i)′ in the medium 61.

sin θ_(i)=n sin θ_(i)′  (6)

Here, the refractive index of the air layer is 1, and the refractiveindex of the glass and liquid crystal is n. θ_(i) is an incident anglein the air layer, and θ_(i)′ is an incident angle in the liquid crystallayer.

FIG. 22 is a diagram depicting the relationship between the intensity oflight f (θ_(i)′) to enter the reflector 61 and the incident angleθ_(i)′, calculated by substituting the formula (6) for the formula (5).Here the light intensity was calculated as I (θ_(i), φ_(i))=1. As FIG.22 shows, if a uniform diffuse light from an integrating sphere isassumed, the intensity of the incident light to the reflector 60increases as the incident angle from the incident angle θ_(i)′=0increases, the intensity of the incident light becomes the maximum in acertain range of the incident angle θ_(i)′ and the incident lightintensity attenuates considerably at around the incident angle 45°. Inother words, an incident angle θ_(i)′ at which the incident lightintensity becomes maximum, exists, and the incident angle differsdepending on the refractive index n of the medium.

FIG. 23 is a diagram depicting the relationship between the incidentangle θ_(i)′, when the incident light intensity in FIG. 22 becomes themaximum, and the refractive index n of the medium. As FIG. 23 shows, asthe refractive index n of the liquid crystal increases, the incidentangle θ_(i)′, when the incident light intensity becomes the maximum,decreases. Since the typical refractive index of a liquid crystal isabout 1.4-1.8, the incident angle θ_(i)′, when the incident lightintensity becomes the maximum, is about 30-38°.

Next we will examine an incident light having the incident lightintensity distribution shown in FIG. 22, which reflects on the inclinedfaces of the undulation of the reflector 61. FIG. 24 is a diagramdepicting the relationship between the incident angle, reflection angleand inclination angle with respect to the inclined face of a reflectionbump. The incident light and reflected light are symmetrical withrespect to a line perpendicular to the inclined face, and a localincident angle α on the micro-mirror face is equal to a local reflectionangle β, so the inclination angle ξ, incident angle θ_(i)′, andreflection angle θ_(o)′, have the following relationship.

2ξ=θ_(i)′+θ_(o)′  (7)

Generally a display is often observed in a direction perpendicular tothe display panel. So when light which enters the reflector havingundulation at the incident angle θ_(i)′ is reflected in the 0°direction, the formula (7) becomes ξ=θ_(i)′/2. In other words, light canbe reflected in a direction perpendicular to the display panel when theinclination angle ξ is ½ of the incident angle θ_(i)′.

As FIG. 22 shows, the distribution of the incident light which entersthe bump faces of the reflector with respect to the diffuse light of theintegrating sphere has a peak in incident angle area 0-45°. Therefore itis preferable to set the distribution of the inclined faces of theundulation faces of the reflector to a distribution corresponding to thelight intensity distribution in FIG. 22. In other words, it ispreferable that the existence probability of the inclination anglescorresponding to the incident angles at which light intensity is high isincreased, and the existence probability of the inclination anglescorresponding to the incident angles at which light intensity is low isdecreased, so that the over all reflected light intensity is increased.

FIG. 25 is a diagram depicting the distribution of existence probabilityof the inclination angle corresponding to the incident light intensitydistribution in FIG. 22. The example in FIG. 25 shows the case when therefractive index n=1.5 in FIG. 22, and is standardized so that the totalsum of the probability becomes 1. The abscissa indicates the inclinationangle % of the reflection bump face, and the ordinate indicates theexistence probability (%). Here, the reflectance of a sample which hasthe existence probability distribution of the inclination angle shown inFIG. 25 when the inclination angle at which the existence probability isthe maximum is determined. FIG. 26 shows the simulation result of suchrefraction characteristics. Specifically, the inclination angle at whichthe existence probability is at the maximum is changed by changing thewidth W of the distribution shown in FIG. 25, and reflectance Y at thistime was computed.

As FIG. 26 shows, the range of the inclination angle ξ (=θ_(i)′/2) atwhich the existence probability is the maximum is the range where thereflectance is the highest in the area of ξ=about 15-19° (θ_(i)′=about30-38°). In other words, in order to increase over all reflectance, itis preferable to maximize the existence probability of the inclinationangle ξ=15-19°, at which the incident light with incident angleθ_(i)′=30-38°, where the incident light intensity shown in FIG. 22 has apeak value, and can be reflected in a direction perpendicular to thedisplay panel.

As described above, in order to reflect light effectively under theuniform diffused light of the integrating sphere, it is theoreticallyclear that the inclination angle by the undulation for reflection musthave the maximum existence probability in about a 15-19° range.

FIG. 27 is a diagram depicting the result of measuring the reflectancewith respect to the uniform diffused light of an integrating sphereusing an actual prototype sample. In the prototyped reflector, therelationship between the inclination angle ξ_(p) when the existenceprobability is at the maximum and the measured reflectance is shown.

FIG. 28 shows cross-sectional views depicting a method of forming thereflector prototype. As FIG. 28A shows, resist (LC-200 made by Shipley)63 is spin-coated on the glass substrate 62 for 20 seconds at 1000-2000rpm. After pre-baking for 30 minutes at 90° C., UV exposure is performedusing the mask 64, as shown in FIG. 28B. Then using a developer (MF 319made by Shipley), development is performed so as to form the convexparts on the glass substrate, as shown in FIG. 28C. Then as FIG. 28Dshows, post-bake is executed for 60 minutes at 120-200° C. so as toround the convex parts. Then an aluminum layer 65 is deposited for 200nm, as shown in FIG. 28E, so as to fabricate the reflector.

A liquid crystal layer was formed between the reflector and the glasssubstrate formed as above, and the reflection type liquid crystaldisplay device, as shown in FIG. 28F, is fabricated. Here liquid crystalmaterial MJ 961213 made by Merck was used for the liquid crystal layer,and the thickness thereof was controlled by a spacer with a 3.5 μmdiameter. Then the reflectance when a diffused light is entered using anintegrating sphere into the reflection type liquid crystal displaydevice prototype fabricated like this was measured. Also the inclinationangle distribution of the undulation of the reflector of the prototypeand the inclination angle ξ_(p) at which the existence probabilitybecomes the maximum was determined. FIG. 27 shows the result.

According to this experiment result, a maximum reflectance is obtainedwhen the inclination angle ξ_(p) at which the existence probability isthe maximum is set to around 16-19°. This experiment result roughlysupports the simulation result shown in FIG. 26. Compared with the caseof the 10° inclination angle, which has been regarded as the optimumvalue, the sample which the ξ_(p) inclination angle, at which theexistence probability is at the maximum, is around 16-19° has the higherreflectance.

FIG. 29 shows diagrams depicting examples of the pattern of the mask 64for forming undulation of the reflector. FIG. 29A is an example when thepatterns of circles which sizes are different coexist, and FIG. 29B isan example when polygons, such as a triangle, square, hexagon andoctagon, coexist. The present invention, however, is not limited tothese patterns.

As another example of forming undulation for reflection, a process,where the distribution of thermal deformation characteristics is formedby irradiating UV as shown in FIGS. 3-6 and micro-grooves are formed byfinal baking thereafter, can be used. The bump shape of themicro-grooves can be controlled by the above mentioned processconditions, so the bump shape is controlled so that the inclinationangle ξ_(p) at which the existence probability is the maximum becomesaround 15-19°.

In the present embodiment, the inclination angles of the undulation ofthe reflector distribute in at least a 0°-25° range, and the existenceprobability is the maximum at around 15-19°, so a reflection liquidcrystal display device having higher reflectance in various environmentscan be provided.

[Control of Inclination Angle Distribution of Reflector (2)]

FIG. 30 is a diagram depicting the distribution of the inclinationangles of the undulation of the reflector to obtain high reflectancewith respect to the diffused light of the above mentioned integratingsphere. The abscissa indicates the inclination angle ξ, and the ordinateindicates the existence probability thereof. As described above, it ispreferable that the existence probability of the inclination angles be adistribution such that the incident light of the incident angle, atwhich the incident intensity to the reflector is high, is reflected morein a direction perpendicular to the display panel. FIG. 30 shows adistribution where the existence probability of inclination anglesaround +15-19° and inclination angles around −15-19° is at the maximum.The + side and the − side exist because when the inclination angle isviewed from a predetermined direction of the display panel, theinclination angle of the incident light from one direction is shown atthe + side, and the inclination angle of the incident light from theopposite direction is shown at the − side. Therefore if the distributiondiagram in FIG. 30 is folded with the inclination angle 0° as thecenter, the inclination angle distribution becomes as shown in FIG. 25.

A liquid crystal display is often used as a display panel of a notebookpersonal computer. FIG. 31 is a diagram depicting a state when thereflection type liquid crystal display device is mounted as the monitorof a notebook personal computer. As FIG. 31 shows, the reflection typeliquid crystal display device 70 is often used in a state where angle θis inclined from the horizontal direction. In this case, the displaydevice 70 is a plane perpendicular to the paper face, as shown in FIG.31. The directions of the X, Y and Z axes are defined as illustratedhere.

Considering incident light to the display device 70, the incident angleθ_(i) distribution along the XY plane of the coordinate isθ_(i)=−90-90°, since nothing blocks incident light. The incident angledistribution along the XZ plane of the coordinate, on the other hand, isnot always θ_(i)=−90-90°, since incident light is blocked by thekeyboard part. In other words, the incident angle range differs betweenthe highest position 70A and the lowest position 70B of the displaydevice 70. The highest position 70A has the widest incident angle range,θ_(i)=−90-α+β°, and the lowest position 70B has the narrowest incidentangle range, θ_(i)=−90-α°.

Therefore, in the incident lights in the XZ plane direction along thedirection perpendicular to the display panel, almost no light entersfrom the incident angle α-90° (or α+β°-90°). Therefore for theinclination angle of the micro-mirror faces arranged in the XZ planedirection of the display panel, incident angles for reflecting theincident light, which enters from this angle range, to the normal line(0°) direction of the display panel, are unnecessary.

For example, if the inclination of the display panel is α=30° and therefractive index of the liquid crystal layer and the glass substrate isn_(LC)=1.5, then the inclination angle for reflecting light which entersat 30-90° to the 0° normal line direction is 10-21°, according to theabove formulas (6) and (7). In other words, an inclination angle in a10-21° range is unnecessary for the inclination distribution ofundulation in a direction perpendicular to the display panel (XZ planedirection).

Therefore it is desirable that the distribution of the inclinationangles in the XY plane direction and the XZ plane direction are as shownin FIG. 32. In other words, the inclination angle distribution in the XYplane direction is the same as the distribution shown in FIG. 30, andfor the inclination angle distribution in the XZ plane direction, the −side is the same as in FIG. 30, and the + side is distribution whichdoes not exist in a 10-21° range. FIG. 33 shows the distribution whenthe distribution in FIG. 32 is folded with the inclination angle 0° asthe center.

FIG. 33 shows the inclination angle distribution formed by theundulation of the reflector, including the distribution in the inclinedface in the XY plane direction, and distribution in the inclined face inthe XZ plane direction. As FIG. 33 shows, when a notebook personalcomputer is tilted and used, it is preferable that the distribution ofthe inclined face in the horizontal direction in the display panel isset such that the existence probability is the maximum in a 15-19°inclination angle range, and the distribution of the inclined face inthe vertical direction in the display panel is set such that theexistence probability has a peak in an 8-10° inclination angle range,and in a 15-19° inclination angle range. In this way, if the angledistribution of the inclined face by reflection undulation is set suchthat one direction has one peak of existence probability and anotherdirection has two peaks of existence probability according to thedirection of the display panel, maximum reflectance can be implemented,even if the display panel is used in an environment which has anisotropyin the incident light direction.

The present inventors manufactured a reflector prototype with the abovementioned inclined face distribution, and confirmed the reflectancethereof. FIG. 34 shows cross-sectional views depicting a method offorming this reflector sample. As FIG. 34A shows, resist (e.g. LC-200made by Shipley) 63 is spin-coated on the glass substrate 62 for 20seconds at 1000 rpm. After pre-baking for 20 minutes at 90°, UV exposureis performed using the mask 64, as shown in FIG. 34B. Then using adeveloper (e.g. MF 319 made by Shipley), development is performed, andconvex parts are formed by resist on the glass substrate, as shown inFIG. 34C. The processes in FIG. 34A-34C are repeated four times bysequentially using the mask patterns (a)-(d) shown in FIG. 35, so as toform convex parts which inclination angles are different, as shown inFIG. 34D. Then as FIG. 34E shows, a post-bake is performed for 80minutes at 200° C. so as to round the convex parts. Then aluminum 66 isdeposited for 200 nm, as shown in FIG. 34F, so as to fabricate thereflector.

FIG. 36 shows a plane shape and cross-sectional shape depicting anexample of the convex part of the reflector formed as above. The planeshape of the convex part 67 has different inclined faces in the verticaldirection V of the substrate 62, and has the same inclined faces in thehorizontal direction H of the substrate 62. In the plan view shown inFIG. 36, contour lines are shown in the convex part 67 so as to show theshape of the inclined face thereof. Since the convex part is rounded bythe post-bake, the inclination angle distribution is in about a 0-20°range. And in the vertical direction V of the substrate, inclined faces(ξ1>ξ2) are different, so there are two areas where the existenceprobability is at a peak, as shown in FIG. 33, and in the horizontaldirection H of the substrate, the inclined face (ξ1) is symmetrical, sothere is one area where the existence probability is at a peak, as shownin FIG. 33.

By changing the direction of the undulation for reflection between thehorizontal direction and the vertical direction as above, thedistribution of the inclination angle in the horizontal direction andthe distribution of the inclination angle in the vertical direction canbe different. As FIG. 36 shows, the distribution of the inclinationangles in the horizontal direction and the inclination angles in thevertical direction can be different from each other by combining asemi-circular shape and semi-elliptical shape, as shown in FIG. 36.

The present inventors measured the shape using a non-contactthree-dimensional shaped measurement device, nh-3, made by Hishiko, anddetermined the inclination distribution of the reflector prototype. FIG.37 shows the measurement result of the inclination angle distribution ofthe reflector prototype. As FIG. 37 shows, the reflector prototype hasthe maximum existence probability at absolute values 8° and 18°. Forcomparison, FIG. 37 also shows the inclination angle distribution of areflector which maximum existence probability is at 0° and 10°, and alsoshows the inclination angle distribution of prior art 1 and prior art 2respectively.

FIG. 38 is a rough cross-sectional view of the reflection type liquidcrystal display device created using the above mentioned reflectorprototype. The liquid crystal layer (e.g. liquid crystal material MJ961213 made by Merck) is injected between the reflector and the glasssubstrate while controlling the thickness with a 3.5 μm diameter spacer.The reflection type liquid crystal display device is secured in a stateinclining 30° with respect to a vertical direction, uniform diffusedlight of the integrating sphere is irradiated, and reflectance wasmeasured using a luminance meter (e.g. BM-5 made by Topcon). FIG. 39shows the measurement result of the reflectance thereof. As FIG. 39shows, if the reflector of the present invention is used, reflectance is61%, where the reflectance improved 10-25% compared with 31% and 53% ofthe prior arts 1 and 2.

FIG. 33 shows the ideal inclination angle distribution where therefractive index n of the liquid crystal layer and the glass substrateis 1.5, and the angle with respect to the horizontal line of thereflection type liquid crystal display device (inclination angle α shownin FIG. 31) is α=30°. When the refractive index n_(LC) of the liquidcrystal layer and the inclination angle α of the reflection liquidcrystal display device are changed, the inclination angle range when theexistence probability is at the maximum in the ideal undulation forreflection was examined respectively.

FIG. 40 is a diagram depicting the inclination angle α of a reflectiontype liquid crystal display device, and the inclination angle range whenthe existence probability becomes the maximum with respect to therefractive index of the liquid crystal layer. Since the refractive indexn_(LC) of a typical liquid crystal material is 1.4-1.8, the refractiveindex n_(LC) was changed in a 1.4-1.8 range. In a general use case, theinclination α tends to increase as the size of the reflection typeliquid crystal display device size decreases, and the inclination α ofthe display panel is changed in a 0-45° range.

When the inclination angle α of the display panel is 30°, as shown inFIGS. 32 and 33, it is desirable that the existence probability of theinclination angle of the undulation becomes the maximum in a 15-19°range on one hand, and the existence probability of the inclinationsangles of the undulation becomes the maximum in two ranges, 8-10° and15-19° on the other hand. In the case when the inclination angle α ofthe display panel is 0°, that is the case when the display panel is setvertically, for the inclination angle ξ of the display panel in thevertical direction, the existence probability of the inclination anglesof the undulation is the maximum in a 15-19° range, since mainly theincident light from above is reflected in the vertical direction. Andthere is little incident light coming from the bottom, so an inclinedface inclining downward is unnecessary. In the case when the inclinationangle α of the display panel is 90°, that is the case when the displaypanel is set horizontally, it is preferable that the existenceprobability of the inclination angles of the undulation is at themaximum in a 15-19° range, although this is not shown in FIG. 40. Thecase when the display panel is horizontal is the same as thedistribution example shown in FIG. 30.

As FIG. 40 shows, when the inclination angle α of the display panel isin a 0-45° range, the reflectance can be at the maximum if oneinclination angle where the existence probability in the undulation forreflection is at the maximum is 0-16°, and the other inclination angleis in a 14-19° range. As the refractive index n_(LC) is smaller, theinclination angle to be at the maximum tends to increase.

For a notebook personal computer, the inclination of the display paneldiffers depending on the user. So it is desirable to form a plurality ofareas, where the existence probability of the inclination angle of theundulation for reflection is at the maximum, in the pixel area, so thatthe maximum reflectance can be implemented at a plurality ofinclinations. For example, as FIG. 40 shows, a first combination of8-10° and 15-19° and a second combination of 10-12° and 15-19° coexistin the same pixel area, as an inclination angle area where the existenceprobability is at the maximum, which was determined corresponding tocases when the inclination angle α of the display device is 30° and 40°.Or three combined areas determined corresponding to cases when theinclination angle α of the display device is 30°, 35° and 40°, and whichcoexist. Or three convex patterns coexist. By this, a relatively largereflectance can be implemented even if the inclination angle of displaypanels are somewhat different.

Using a reflection electrode having the above mentioned inclinationangle distribution of undulation for reflection for a pixel electrode,the reflection type liquid crystal display device with the structureshown in FIG. 2 is formed, and a desired display can be implemented byapplying a predetermined electric field from the pixel electrode and thetransparent electrode of the display side to the liquid crystal layer34, so as to provide a double detraction function to the liquid crystallayer 34. In other words, the liquid crystal layer 34 is driven in fieldeffect double detraction mode. Also, a guest-host type liquid crystaldisplay device can be implemented by including dye into the liquidcrystal layer 34.

[Example of Undulation for Reflection where Different DirectivitiesCoexist]

Japanese Patent Laid-Open No. H11-295750 discloses a reflection typeliquid crystal display device which uses a pixel electrode as areflection electrode. According to this disclosure, the pixel electrodeis divided into two areas, bump shapes having reflection characteristicswith strong directivity are formed in one area, and bump shapes havingreflection characteristics with strong diffusibility are formed in theother area.

However, in the case of a higher precision liquid crystal displaydevice, the pixel area becomes smaller, and it is probably difficult toform different bump shapes respectively for the pixel areas divided intotwo, as seen in the prior art.

Therefore in the present invention, bump shapes having reflectancecharacteristics with strong directivity and bump shapes havingreflection characteristics with strong diffusibility coexist in a pixelarea. FIG. 41 is a cross-sectional view depicting two reflection bumpshapes coexisting in such a pixel area. Bump A has a gentle inclinedface with a thin film thickness, where the top face is relatively flat,so reflected light is directed to the vertical direction. And bump B, onthe other hand, has a sharp inclined face with thick film thickness, thetop face protrudes, so reflected light diffuses widely.

FIG. 42 is a plan view of the pixel area PX in the present embodiment.As illustrated, bump A and bump B, shown in FIG. 41, coexist in thepixel area PX.

FIG. 43 shows cross-sectional views depicting the manufacturing processfor forming the undulation for reflection in FIG. 42. At first, as FIG.43A shows, resist (e.g. LC-200 made by Shipley), which is aphoto-sensitive resin, is spin-coated for 20 seconds at 2000 rpm on theglass substrate 62. After pre-bake is performed for 20 minutes at 90°C., UV exposure is performed using the mask 64A shown in FIG. 43B. Thenusing a developer (e.g. MF 319 made by Shipley), development isperformed so as to form the convex part corresponding to bump A on theglass substrate 62, as shown in FIG. 43C. Then, as FIG. 43D shows, apost-bake is executed for 80 minutes at 200° C., so as to round theconvex part to form bump A.

Then as FIG. 43E shows, the resist is spin-coated for 20 seconds at 1000rpm. By this, a resist layer thicker than the above mentioned resist canbe formed. After pre-baking for 20 minutes at 90° C., UV exposure isperformed using the mask 64B, as shown in FIG. 43F. Then development isperformed using the above mentioned developer, and a convex partcorresponding to bump B is formed on the glass substrate, as shown inFIG. 43G. Then a post-bake is performed for 80 minutes at 200° C., asshown in FIG. 43H to round the convex part, and bump B is formed. Sincethis post bake is performed at a temperature lower than that for formingbump A, sagging of the thick resist film by heating is less, and bump Bwith stronger diffusibilty can be formed.

Then as FIG. 43I shows, the reflector (pixel electrode) is fabricated bydepositing aluminum 64 for 200 nm. As mentioned above, the roundness ofthe undulation can be changed by changing the resist film thickness andthe post-bake temperature between bump A and bump B, and a reflectionface, where undulation with different directivity during scatteringcoexist, can be created.

As mentioned above, it is preferable that the reflector of thereflection type liquid crystal display device reflect incident lightfrom various directions to a direction perpendicular to the displayface. Therefore, when the resist layer is patterned and rounded bybaking to form the inclined face, it is preferable that the inclinedface direct 360°. Therefore a circular pattern has been proposed as apattern of the resist film. Examples are disclosed in Japanese PatentLaid-Open No. H11-337935, Japanese Patent Laid-Open No. H11-337964, andJapanese Patent Laid-Open No. H5-281533. These patents proposed formingthe circular patterns at random so as to prevent the formation of moirépatterns by the interference of reflected light, or forming doughnutpatterns with a large radius and small circular patterns with a smallradius at random, so as to improve the reflection characteristics.

Japanese Patent Laid-Open No. H5-281533 discloses forming coexistinglarge circular patterns and small circular patterns at random. Anexample is shown in FIG. 44. However, if large circular patterns with alarge radius are arranged at random, adjacent resist patterns unite bysagging in a cross-sectional shape by heating during the post-bakingprocess after exposure and development. The shaded circular patternsshown in FIG. 44 show the state when the patterns are too close to eachother, and which unite during baking.

So in the present embodiment, as FIG. 45 shows, the circular patternswith a large radius and circular patterns with a small radius coexist inthe resist pattern, and are arranged such that the distance between alarge circular pattern and a small circular pattern is always smallerthan the distance between large circular patterns. In other words, alarge circular pattern coming too close to another large circularpattern is prevented. If possible, small circular patterns are arrangedaround a large circular pattern, so that large circular patterns do notcome close to each other. By this, the density of an inclined face canbe increased, and areas where patterns are united during baking can bedecreased.

FIG. 46 shows diagrams depicting the resist pattern of the presentembodiment.

FIG. 46A is an example when relatively large circular patterns arearranged. Four large circular patterns P1 are arranged in the pixel areaPX. The resist pattern must have a certain size. If the pattern is toosmall, the inclination angle will be insufficient because of sagging inthe cross-sectional shape during post-bake. In the case of the patternin FIG. 46A, however, reflectance cannot be increased since the densityof the inclined face to be formed is low.

As FIG. 46B shows, it is possible to increase the density of the largecircular patterns P1. However, if the large circular patterns P1 cometoo close to each other, the edges of the circular patterns may unite,as shown by shading, because of sagging by heat during post-bake. Such auniting decreases the area of the inclined face to be designed, which isnot desirable.

As in the present embodiment, the density of the relatively largecircular patterns P1 is not dense, as shown in FIG. 46A, and thedistance L1 between the patterns P1 is maintained to be relativelylarge, and the relatively small circular patterns P2 are arranged in thespace between the large circular patterns P1, so as to increase thedensity of the inclined faces, as described referring to FIG. 45 and asshown in FIG. 46C. By this, the relatively large circular patterns donot unite with each other, and even if they do unite, this is limited tothe space between a large circular pattern P1 and a small circularpattern P2 (shaded area in FIG. 46C). Such a united area is relativelysmall compared with the united area between the large circular patternsP1, and the decrease of the inclined face area can be minimized.

As FIG. 46C shows, the distance L1 between the large circular patternsP1 is long enough not to cause uniting, and the small circular patternsP2 are arranged in the areas between the circular patterns P1. As aresult, the distance L2 between the large circular pattern P1 and thesmall circular pattern P2, which is closest to P1, is always shorterthan the distance L1 between the large circular pattern P1 and the largecircular pattern L1 closest thereto.

FIG. 47 is a diagram depicting another resist pattern. The above exampleuses circular patterns so that the inclined face of the undulation forreflection turn in 360° directions, but a polygon, which sides direct aplurality of directions, preferably three or more, instead of a circle,can implement a similar high reflectance.

FIG. 47 is an example of a pattern of resist where many hexagons arearranged close to each other so that adjacent sides are parallel to eachother in the pixel area PX. At the edge of the pixel area PX, an entirehexagon cannot fit, and trapezoids and pentagons are arranged, butbasically hexagons are arranged like tiles in this resist pattern. Byarranging each side to be in parallel, uniting during post-bake can beprevented even if a hexagon comes very close to another.

Using such a mask pattern, the resist layer is exposed and developed,and post-bake is executed, then the cross-sectional shape sags due toheat, and undulation for reflection, which has an inclined face inclinedin at least three directions, can be formed.

FIG. 48 is a diagram depicting another resist pattern. In the example inFIG. 48, not hexagons but a plurality of equilateral triangles arearranged such that each side comes close to another in parallel. In thiscase as well, the resist layer is exposed and developed, and post-bakeis executed, then the cross-sectional shape sags due to heat, andundulation for reflection, which has inclined faces inclining in atleast three directions, can be formed. The present embodiment can formthe undulation for reflection having inclined faces at high density evenif another polygon shape is used.

The process of forming the undulation for reflection using the patternsin FIGS. 45, 47 and 48 is the same as the process shown in FIG. 28. Forthe mask 64 in the exposure process of the resist layer, the patterns inFIGS. 45, 47 and 48 are used. By this, high density inclined facedistribution can be formed without allowing to patterns unite with eachother, and the reflectance of the reflector can be increased.

[Embodiment of Guest-Host Liquid Crystal Layer]

The rough configuration of the reflection liquid crystal display deviceof the present embodiment is the same as FIG. 2. In this embodiment,however, a guest-host liquid crystal layer where dichroic dye are mixedin the liquid crystal is used.

[Forming Undulation by Half Exposure]

The main point of the present embodiment is that in order to controlundulation shapes on the surface of the reflection layer, the reflectionlayer is configured such that the reflected light scattering width inthe incident plane when parallel light enters depends on the azimuth ofincident light, by forming a light absorption layer which lightabsorption characteristics depend on the azimuth in the front face ofthe reflection layer, and bump shapes on the surface of the reflectionlayer are controlled by adjusting such that the azimuth, when thereflection light scattering width is at the maximum, and the azimuthwhen the light absorption of the light absorption layer is at themaximum or at the minimum, roughly match.

[Concrete Configuration]

Fabrication Example 1

As FIG. 83 shows, we fabricated diffuse reflectors comprised of (a) acircular pattern, (b) an elliptical pattern, (c) a trapezoidal pattern,(d) a cocoon-shaped pattern, and (e) a wrinkle pattern.

The circular, elliptical, trapezoidal and cocoon-shaped patterns werefabricated as follows. Resist AFP 750 (made by Shipley) was coated on a0.7 mm thick glass substrate to be 3 μm, then using a mask pattern wherecircular, elliptical, trapezoidal or cocoon-shaped patterns are arrangedat random, half exposure was performed at a 80 mJ/cm² exposure energy.After the half exposure and development, bake is performed for 40minutes at 135° C., so that each pattern is smoothed by heat andinclination is controlled. Then bake is performed for 1 hour at 200° C.to completely cure the resist, and the reflector was fabricated byvacuum deposition of Al on the resist to be about a 200 nm thickness.

For the wrinkle patterns of the micro-grooves, resist AFP 750 was coatedon the 0.7 mm thick glass substrate to be 3 μm, and UV with a 3900mJ/cm² exposure energy was irradiated. After UV irradiation, bake wasperformed for 90 minutes at 135° C. to generate fine wrinkles on theresist surface. Then final bake was performed for 1 hour at 200° C., andthe reflector was fabricated by vacuum deposition of Al on the resist tobe about a 200 nm thickness.

To generate more wrinkle patterns in a predetermined direction, arectangular transparent electrode made of indium tin oxide (ITO) wasformed on the glass substrate.

By using this pattern, more wrinkles are generated in a directionparallel with the sides of the ITO rectangle (azimuth: 0-180° and90-270°).

Parallel lights are entered into these reflectors changing incidentangles, and the reflection characteristics in a 0° direction weremeasured.

FIG. 84 shows the result of measuring the reflection characteristics.This shows the reflectance on the ordinate when the polar angle of theincident light (incident angle on the abscissa) and the azimuth angleare changed.

As FIG. 84 shows, the reflection characteristics do not depend onazimuth (shown in rectangular) in the case of a circular pattern, but inthe case of an elliptical, trapezoidal, cocoon-shape and wrinklepatterns, the reflection characteristics change considerably dependingon the azimuth. In other words, in the case of elliptical, trapezoidaland cocoon-shaped patterns, the scattering width is wider in the minoraxis direction than the major axis direction, and in the case of awrinkle pattern, the scattering width in a direction parallel with thesides of the ITO rectangle is wider than that of other directions.

Therefore it is preferable to select an optimum pattern according to theintended use of the liquid crystal display panel.

Fabrication Example 2

Dichroic dye MA 981103 (made by Mitsubishi Chemical) was mixed into then-type liquid crystal MJ 95785 (made by Merck), the density of the dyewas changed to obtain contrast 5, and the relationship between the twistangle and the reflectance of the liquid crystal layer was examined.

FIG. 85 shows the result.

As FIG. 85 shows, a brighter reflectance is obtained as the cellthickness decreases, and a maximum reflectance is obtained at a 180°twist or 330° twist. However, if a 330° twist is implemented, thevoltage reflectance characteristics has hysteresis, so generally thetwist angle must be 240° or less. So we examined the viewing anglecharacteristics of the bright state and the dark state of the reflectionguest-host liquid crystal when the cell thickness of the guest-hostliquid crystal is 3 μm, and a 180° twist structure was created byperforming parallel rubbing processing in the azimuth 0° of the top andbottom substrates.

FIG. 86 shows the result.

In the bright state, the reflection characteristics do not changebetween the azimuth 0° direction and the azimuth 90° direction, so thereflection characteristics do not depend on the azimuth, but in the darkstate, the characteristics differ considerably between the azimuth 0°direction and the azimuth 90° direction. In other words, the lightabsorption characteristics depend on the azimuth in the dark state,where absorption in the larger incident angles is higher in the azimuth0° direction than in the azimuth 90° direction.

In the case of an elliptical pattern, for example, fabricated in thefabrication example 1, the reflection characteristics depend on theazimuth angle.

Here a guest-host liquid crystal, which is twisted 1800, is considered,as FIG. 87 shows. When the intensity of light, which enters at incidentangle θ and azimuth angle φ is IO (θ, φ), the guest-host layertransmittance of light which enters at incident angle θ and azimuthangle φ is T (θ,φ), and the reflectance of the reflector when the lightat incident angle θ and azimuth angle φ reflects in the 0° direction isR (θ, φ). The light intensity I (θ, φ) when the light enters thereflection guest-host liquid crystal at incident angle θ and azimuthangle φ and is reflected in the 0° direction is given by the followingformula.

I(θ, φ)=I ₀(θ, φ)·T(θ, φ)·R(θ, φ)·T(θ=0°, φ=0°)  (11)

Since light enters from various directions in an environment where areflection type liquid crystal display device is used, it is necessaryto assume that light which enters at incident angle θ actually entersfrom all azimuths. When light at incident angle θ enters from allazimuths, formula 1 is integrated for all azimuths, but an approximatelight value can be given by an average value of the azimuth φ and anazimuth perpendicular thereto, φ+90°. (To obtain a more accurate value,increase the number of azimuths and average the values).

In the case of an elliptical pattern, for example, azimuth 0° and 180°,and 90° and 270° are almost the same, so light from all azimuths can beapproximated by the sum of the azimuth 0° direction and the azimuth 90°direction, as shown in the formula (12).

I(θ, φ)≈(½)I ₀(θ, φ=0°)·T(θ=0°, φ=0°)·[T(θ=0°, φ=0°)·R(θ, φ=0°)+T(θ,φ=90°)·R(θ, φ=90°)  (12)

So we estimated the reflectance based on the formula (12) for the casewhen a diffuse reflector with an elliptical pattern and a guest-hostliquid crystal are combined. Table 4 shows the result when thereflectance was calculated by the formula (12) for the case when themajor axis of the ellipse and the rubbing direction are the same (case1), the case when the minor axis of the ellipse and the rubbingdirection are the same (case 2), and the case when a circular reflectoris used (case 3). Reflectance and contrast were calculated in Table 4.As Table 4 shows, contrast is higher in the elliptical pattern than inthe circular pattern, and especially under the conditions of case 2,contrast increased considerably.

TABLE 4 Reflectance estimation result Bright state Dark state Contrast θ= 30° 45° 60° θ = 30° 45° 60° θ = 30° 45° 60° Case 1 74.7% 32.9% 3.6%16.2% 5.9% 0.9% 4.6 5.6 4.0 Case 2 74.7% 32.9% 3.6% 16.1% 5.3% 0.2% 4.66.2 18.0 Case 3 75.2% 32.9% 3.5% 16.4% 8.4% 1.3% 4.6 4.3 2.7

In other words, as FIG. 87 shows, contrast increases considerably bymaking the minor axis of the ellipse and the rubbing direction the same.

We actually fabricated cells for each case 1-3. Dichroic dye MA 981103is mixed at 4.3 wt % to liquid crystal MJ 95785, and the amount ofmixing chiral material CB-15 (made by Merck) was adjusted so that thechiral pitch becomes 8 μm. The cells were implemented by sealing thisguest-host liquid crystal into the cells using a 4 μm diameter spacer.

Considering the environment where a reflection liquid crystal displaydevice is used, the reflection characteristics and the contrast weremeasured using an integrating sphere. Table 5 shows the result. As Table5 shows, it was confirmed that contrast becomes higher than the case 3which is the conventional approach, by structuring an actual cell, as incase 2.

TABLE 5 Integrating sphere measurement result Reflectance Contrast Case1 44.2% 5.3 Case 2 44.2% 6.2 Case 3 45.2% 5.1

A similar result was obtained when trapezoidal, cocoon-shaped andwrinkled patterns were used as the bump pattern of a diffusionreflector, and high contrast characteristics were obtained by combiningthe axis of a guest-host liquid crystal and azimuth of a reflectorappropriately.

Fabrication Example 3

FIG. 88 shows the result of measuring the incident light anglecharacteristics of polarizer G 1220 DU (made by Nitto Denko). Theazimuth 0° is the direction of absorption axis of the polarizer, and theazimuth 90° is the direction of the transmission axis.

As FIG. 88 shows, the transmission axis direction (azimuth 90°) has ahigher transmittance in a wide angle range than the absorption axisdirection (azimuth 0°). So this polarizer is optically contacted to theelliptical pattern, and the reflectance was measured using anintegrating sphere.

Table 6 shows the measurement result. Case 1 is when the major axisdirection of the elliptical pattern and the absorption axis direction ofthe polarizer are matched, and case 2 is when the minor axis directionof the elliptical pattern and the transmission axis direction of thepolarizer are matched. As Table 6 shows, it was confirmed that case 1can implement a higher reflectance than case 2.

TABLE 6 Reflection characteristics when polarizer G 1120 DU andelliptical reflector are combined (integrating sphere) Reflectance Case1 38.2% Case 2 36.5%

Therefore as FIG. 89 shows, one polarizer type reflection liquid crystaldisplay device was fabricated by layering liquid crystal layer 402(FT-5045LE (made by Chisso)), λ/4 plate 403, λ/2 plate 404, andpolarizer 405 (G1220DU) on the diffuse reflector 401. Table 7 shows thereflectance and the contrast characteristics measured using anintegrating sphere.

TABLE 7 Reflectance and contrast of one polarizer type (integratingsphere) Reflectance Contrast Case 1 35.3% 17.5 Case 2 34.1% 17.1 Case 335.1% 17.2

Here case 1 is when the major axis direction of the elliptical patternand the absorption axis direction of the polarizer are matched, case 2is when the minor axis direction of the elliptical pattern and thetransmission axis direction of the polarizer are matched, and case 3 iswhen a circular pattern diffuse reflector is used. As Table 7 shows,compared with case 3 which is prior art, the reflectance increasedsomewhat in case 1. In other words, in the case of a polarizer type aswell, the reflectance improved by combining the axis of the polarizerand the azimuth of the reflector appropriately.

As described, according to the present embodiment, a reflectionelectrode, which can implement stable high reflectance characteristics,can be formed, and a guest-host type and one polarizer type reflectionliquid crystal display devices with high reliability, which allows adisplay with high lightness, can be implemented.

[Front Light Structure]

The reflection type liquid crystal display device lights the displayface by reflecting external light without disposing backlight.Therefore, the reflection type liquid crystal display device has lowpower consumption and is useful as a display panel of portableinformation terminals and portable telephones. However, use is limitedto a bright place, since external light is used. So a liquid crystaldisplay device with a front light which is turned on only when the unitis in use in a dark place has been proposed.

FIG. 49 is a diagram depicting the configuration of a conventionallyproposed reflection type liquid crystal display panel with a frontlight. As FIG. 49 shows, a front light 70 is installed on the displayside of the reflection liquid crystal display panel 73. In thereflection type liquid crystal display panel 73, a liquid crystal layer,which is not illustrated, is inserted between the rear side substrate73B, having a reflector structure, and the display side substrate 73A.And on the display side substrate 73A, the front light 70 is installed,and the front light 70 is comprised of a light source 71 and atransparent substrate 72 which guides the light from the light source tothe entire surface of the display, and scatters the light to the displaypanel 73 side using the scattering layer or the prism layer formed onthe surface. The light of the light source 71 is scattered by thedifference of the refractive index between the scattering layer or theprism layer formed on the surface of the transparent substrate 72 andthe air layer, and a part of the scattered light is scattered to thedisplay panel 73 side.

However, in the case of the reflection type liquid crystal displaydevice configured as in FIG. 49, the scattering layer or the prism layeris formed on the surface of the transparent substrate 72, and anobserver sees characters and images on the display panel 73 via thisscattering layer and prism layer. Therefore characters and images aredistorted or blurred by the scattering layer or the prism layer, whichdrops the image quality.

So the present embodiment has a front light structure such that thetransparent substrate, which guides light only when the light source isturned on, has a scattering characteristic, and the transparentsubstrate does not have this scattering characteristic when the lightsource is not turned on. By using this structure, where the front lightstructure does not use the scattering function when in normal use usingexternal light, characters and images observed on the display panel arenot distorted or blurred. Only in limited cases, such as use in a darkplace, the front light structure provides light from the light sourcevia the scattering characteristic, so the display panel is brightenedand minimum functions required as the display panel can be secured, evenif characters and images are somewhat distorted and blurred.

FIG. 50 shows diagrams depicting a first example of the front light. Thefront light 70 shown in FIG. 50 comprises a transparent substrate 74,where the surface of a transparent substrate made of acrylic issand-blasted so as to form a scattering layer 75 on the surface, atransparent substrate 76 made of acrylic, a fluid 77, such as siliconoil to be filled between the substrates, a fluid pump 78 and a fluidtank 79. The front light 70 further comprises a linear light source 71made of a cold cathode fluorescent tube. Between the substrates 74 and76, the fluid stored in the fluid tank 79 is filled in or taken out bythe fluid pump 78. The refractive index of this fluid 77 is n=1.5, whichis roughly the same as the transparent substrates 74 and 76.

As FIG. 50A shows, when the reflection liquid crystal display panel isused in a bright place, the light source 71 is in the off state, and thefluid 77 is filled into the gap between the transparent substrates 74and 76. By this, an observer cannot see the scattering layer 75 sincethe refractive index is the same as the fluid 77. Therefore when theliquid crystal display panel is used in a bright place, characters andimages on the display panel 73 are not blurred or distorted.

When the reflection liquid crystal display panel is used in a darkplace, on the other hand, the light source is in the on state, and thefluid 77 is taken out of the gap between the transparent substrates 74and 76 by the fluid pump 78, and the air layer is filled into the gap ofthe substrates, as shown in FIG. 50B. Therefore the refractive indexdifference is generated between the acrylic of the transparent substratematerial (refractive index is about 1.5) and air (refractive index of1.0) in the scattering layer 75, and the original function of thescattering layer is presented. So lights which have been guided,repeating internal reflection from the light source 71 which is at theend of the transparent substrates 74 and 76, are scattered by thisscattering layer 75, and lights the reflection liquid crystal displaypanel 73. As a result, a bright display panel can be implemented even ina dark place.

When this front light 70 is viewed from the observer side, thescattering layer 75 of the transparent substrate 74 is seen, and thedisplay of the reflection liquid crystal display panel 73 is distorted.However such distortion is equivalent to that of a conventionalreflection liquid crystal display panel with a front light.

As described above, the same display as a reflection display panelwithout a front light is obtained when used in a bright place, and lightfrom the light source can be used for illuminating the reflection liquidcrystal display panel when used in a dark place, therefore a brightdisplay is implemented.

FIG. 51 shows diagrams depicting a second example of a reflection liquidcrystal display panel with a front light according to the presentembodiment. In this example, a transparent electrode (ITO) 81 whose themain component is indium oxide is formed on the surface of twotransparent substrates 74 and 76 made of glass, for example, and theliquid crystal layer 80, which state changes depending on the electricfield, is sandwiched in the gap between the transparent substrates.Voltage V1 is applied or not applied between the transparent electrodes81 depending on the switch SW. Normally, this liquid crystal layer 80becomes a transparent state when voltage V1 is applied between thetransparent electrodes, and becomes a scattering state when the voltagebetween the transparent electrodes is 0. Therefore in a bright place,the switch SW is turned on to make the liquid crystal layer 80 to betransparent, and in a dark place, the switch SW is turned off to makethe liquid crystal layer 80 to be a scattering state.

The liquid crystal materials for which the scattering state andtransmission state can be switched are (1) a liquid crystal using adynamic scattering effect, (2) a liquid crystal using a phase transitioneffect between the cholesteric phase and the nematic phase, and (3) apolymer dispersion type liquid crystal, and one of these liquid crystalscan be used.

In the case of the example in FIG. 51, compared with the example in FIG.50, a transparent substrate with a scattering layer, pump and tank areunnecessary, where the time for filling and taking out fluid can besaved. Also in the case of the polymer dispersion type liquid crystal,the degree of anisotropy of the refractive index of spherical liquidcrystals in the polymer can be adjusted by applied voltage. Thereforethe degree of scattering of the liquid crystal layer 80 can be adjustedby adjusting the applied voltage, and an observer can adjust the degreeof scattering of the lights from the light source 71 to increase thebrightness, or the degree of scattering of the lights is decreased tocontrol the distortion of the display screen.

Even in the example of FIG. 51, the display of the reflection typeliquid crystal display panel looks as if viewing through frosted glasswhen the light source 71 is turned on and the liquid crystal layer 80has the scattering characteristic, but this is equivalent to aconventional reflection type liquid crystal display panel with a frontlight. And when the light source 71 is off in a bright state, the liquidcrystal layer 80 is transparent, and the display is not blurred ordistorted. In other words, this example, which is a reflection typeliquid crystal display panel with a front light, allows a displayquality equivalent to a reflection type liquid crystal display panelwithout a front light when the front light is not on, and allows adisplay quality equivalent to a normal reflection type liquid crystaldisplay panel with a front panel when the front light is on.

FIG. 52 shows diagrams depicting a third example of a reflection liquidcrystal display panel with a front light. In this example, thetransparent electrode 81 is formed on the inner face of the transparentsubstrates 74 and 76, such as glass, and a prism layer 82 havingprism-shaped fine undulation is formed inside the transparent substrate74. And the liquid crystal layer 80 having refractive index anisotropyis sealed inside the transparent substrates 74 and 76. The moleculealignment direction of the crystal molecules having refractive indexanisotropy is changed by the electric field, and the direction of therefractive index anisotropy changes. Here one refractive index of theliquid crystal layer 80, having refractive index anisotropy, is matchedwith the refractive index of the prism layer 82.

As FIG. 52A shows, when the display panel is used in a bright place,voltage is applied to the liquid crystal layer 80, or no voltage isapplied, so that the refractive index of the prism layer 82 and therefractive index of the liquid crystal layer 80 are matched in thedirection from the display side to the reflection display panel 73. Inthis state, the refractive index of the prism layer 82 and therefractive index of the liquid crystal layer 80 match in the directionfrom the display side to the reflection display panel 73, where ascattering state caused by the prism layer 82 disappears and the frontlight structure becomes transparent. As a result, the state becomes thesame as the state of a reflection type liquid crystal display panelwithout a front light, where the display screen is not blurred ordistorted.

For use in a dark place, on the other hand, no voltage is applied orvoltage is applied to the liquid crystal layer 80, so that therefractive index of the prism layer 82 and the refractive index of theliquid crystal layer 80 are different in the direction from the displayside to the reflection display panel 73, as shown in FIG. 52B. Becauseof this, a refractive index difference is generated at the interfacebetween the prism layer 82 and the liquid crystal layer 80, and lightfrom the light source 71 is refracted. This refracted light becomes theillumination light to the reflection type liquid crystal display panel73, and a bright display can be implemented.

In this example, prism shapes are formed on the surface of thetransparent substrate 74, but a similar effect can be expected byforming a scattering layer on the surface of the transparent substrate74 by a sand-blast process.

By applying this structure, a similar effect as example 2 can beobtained, and a transmission state and scattering state can be switchedmuch faster due to the nature of the liquid crystal layer 80. Alsocompared with the polymer dispersion type liquid crystal in example 2,voltage can be directly applied to the liquid crystal layer 80, so theapplied voltage to the liquid crystal layer 80 can be lower than usingthe polymer dispersion type liquid crystal. And by matching therefractive index of the liquid crystal layer with the refractive indexof the prism layer 82 in a state where voltage is not applied to theliquid crystal layer 80, it is unnecessary to apply voltage to the lightsource 71 and the transparent electrode 81 when the display panel isused in a bright place, which further decreases power consumption.

FIG. 53 shows diagrams depicting a fourth example of a reflection typeliquid crystal display panel with a front light. In this example, thetransparent electrode 81A, which is formed on the transparent substrate74, which is the light guiding plate of the front light 70, is separatedinto strips, so that applying voltage 81A-1 or not applying voltage81A-2 can be selected for each strip. And a liquid crystal layer, whichstate changes depending on whether voltage is applied, is filled betweenthe transparent substrates 74 and 76. FIG. 53A shows a cross-sectionalstructure, and FIG. 53B shows a plane structure of the separatedtransparent electrode 81A.

If this structure is used, the area of the liquid crystal layer to bethe scattering state can be appropriately changed by changing the numberof transparent electrodes 81A to which voltage is applied, and thequantity of illumination light can be adjusted to a certain degree.Therefore in this configuration, the degree of scattering can beadjusted by selecting the transparent electrodes to which voltage isapplied, even if a scattering type liquid crystal where the degree ofscattering cannot be adjusted, a liquid crystal using a dynamicscattering effect, or a liquid crystal using a phase transition effectbetween the cholesteric phase and the nematic phase, is used for theliquid crystal layer 80.

If the degree of scattering by the liquid crystal layer of the frontlight is high, the reflection type liquid crystal display panel with afront light scatters the light from the light source 71 very well, andilluminates the reflection liquid crystal display panel 73 very well,therefore the brightness of the reflection liquid crystal display panelincreases. However, the display image clouds and the resolution dropssince the scattering layer exists between the observer and thereflection type liquid crystal display panel. Therefore, if a degree ofscattering is possible, the observer can adjust it to optimize thedisplay quality for viewing.

FIG. 54 shows diagrams depicting a fifth example of a reflection typeliquid crystal display panel with a front light. In the front light 70of this example, just like the second example shown in FIG. 52, atransparent electrode 81 is formed inside the transparent substrates 74and 76 and the liquid crystal layer 80 is filled between them. Theliquid crystal layer 80 is a polymer dispersion type liquid crystalwhere refractive index anisotropic resin is used for the polymer, and isconfigured such that the normal light refractive index and the abnormallight refractive index of the liquid crystal grains 90 match therefractive index of the polymer in two directions in a state wherevoltage is not applied between the transparent electrodes.

Details of the polymer dispersion type liquid crystal are shown at theright in FIG. 54. While liquid crystal grains 90 having refractive indexanisotropy are dispersed in polymer not having refractive indexanisotropy in the case of polymer dispersion type liquid crystal A,liquid crystal grains 90 having refractive index anisotropy aredispersed in polymer having refractive index anisotropy in the case ofpolymer dispersion type liquid crystal B.

It is assumed that in crystal grains 90, molecules are aligned in thethickness direction of the front light 70, the refractive index in thethickness direction of the front light matches with the polymer 92 andthe transparent substrates 74 and 76 when voltage is not applied betweenthe transparent electrodes, and these refractive indexes do not matchwhen voltage is applied between the transparent electrodes.

In this case, in the polymer dispersion type liquid crystal A, therefractive index of the liquid crystal grains 90 in the verticaldirection match the polymer 92 and the transparent substrates 74 and 76,and lights in the vertical direction do not have a refractive indexdifference, so no refraction and scattering occur. However, thehorizontal refractive index is different between the polymer 92 and theliquid crystal grains 90, so refraction occurs to not only horizontallight but also to diagonal light, that is, to the horizontal directionvector component of the lights. Therefore, when the reflection typeliquid crystal display panel 73 is viewed diagonally, the front panel 70looks clouded, due to this refraction.

If polymer dispersion type liquid crystal B is filled between thetransparent substrates 74 and 76, on the other hand, liquid crystalmolecules align in the thickness direction of the front light whenvoltage is not applied between the transparent electrodes, and thedirection of the refractive index anisotropy of the liquid crystalgrains 90 and the direction of the refractive index anisotropy of thepolymer 92 match. Therefore, in this state, a refractive indexdifference between the liquid crystal grains 90 and the polymer 92 isnot generated at all from any direction, and the front light becomestransparent from all directions. Therefore, compared with the case ofusing polymer dispersion type liquid crystal A, a distortion and foggingof images viewed from a diagonal direction can be prevented when thepanel is used in a bright place of FIG. 54A.

When the panel is used in a dark place and voltage is applied betweenthe transparent electrodes as FIG. 54B, the direction of refractiveindex anisotropy of the liquid crystal grains 90 mismatches with thedirection of the refractive index anisotropy of the polymer 92. This isbecause the direction of the anisotropy of the polymer 92 is not changedby an electric field. Therefore the front light 70 becomes a scatteredstate, and light from the light source 71 is scattered to the reflectiontype liquid crystal display panel 73 side, which brightens the liquidcrystal display surface. However, the color of the liquid crystal layer80 becomes cream-yellow, and blurring and distortion occur to thedisplay screen.

In this case, the direction of the refractive index anisotropy of theliquid crystal grains 90 can be adjusted by adjusting the voltage to beapplied between the transparent electrodes. In other words, if theapplied voltage is increased, the degree of scattering in the liquidcrystal layer increases, incident light to the reflection liquid crystaldisplay panel 73 increases, and the screen brightens, but the screen maybecome too white, making it difficult to view. If the applied voltage isdecreased, on the other hand, the degree of scattering in the liquidcrystal layer decreases, and the screen darkens, but the transparency ofthe screen increases. So by adjusting the applied voltage, the degree ofbrightness of the screen and the degree of contrast can be set as theobserver desires.

FIG. 55 is a diagram depicting a sixth example of a reflection typeliquid crystal display panel with a front light. In the previousexamples in FIGS. 50-54, light from the light source 71 are guided inthe two transparent substrates. Whereas in the example in FIG. 55, thelight source 71 is disposed on the side face of the substrate 74 at thedisplay face side of the two transparent substrates, and light is guidedmainly in the substrate 74 in the display face side. Light is scatteredby the prism-shaped undulation 82 arranged on the side face of thereflection type liquid crystal display panel 73 of the substrate 74, soas to illuminate the reflection type liquid crystal display panel 73. Onthe transparent substrates 74 and 76, a transparent electrode, which isnot illustrated, is formed, and the liquid crystal layer 80 is filledbetween the substrates.

When light is guided in the two transparent substrates 74 and 76 at thetop and the bottom, as shown in FIGS. 50-54, light guided from the topand bottom transparent substrates contact the prism-shaped undulation82. In this case, it is desirable that light from the top transparentsubstrate 74 is refracted, scattered and transmitted downward, and lightfrom the bottom transparent substrate 76 is reflected, scattered andreflected downward as well. However, more light is actually refracted,scattered and transmitted than light reflected, scattered and reflecteddownward, so it is difficult to efficiently reflect and scatter lightfrom the bottom substrate.

Whereas in the case of the configuration in FIG. 55, a prism layer 82 isdisposed at the display panel 73 side of the transparent substrate 74,where light from the light source is transmitted. Therefore lightirradiated to the prism layer 82 is the light transmitted through thetop transparent substrate 74, and more light refracted and scatteredthrough the prism layer 82 enters the reflection type liquid crystaldisplay panel 73 side. Therefore the prism-shaped undulation 82 onlyneeds to be refraction scattering shapes, and a simplification of shapesand an improvement of illumination efficiency can be implemented.

When the liquid crystal layer 80 having scattering characteristics isalso sealed, more light from above is scattered to the liquid crystallayer 80 and is transmitted downward, and the quantity of light to bereflected and scattered is low. Therefore, in the above structure,illumination efficiency is higher. For light from the light source 71,the quantity of incident light from the light source decreases sinceonly one transparent substrate 74 guides light, but the quantity ofincident light from the light source 71 can be improved by increasingthe thickness of the transparent substrate 74.

FIG. 56 is a diagram depicting the seventh example of a reflection typeliquid crystal display panel with a front light. The configuration ofFIG. 56 improves on the structure of FIG. 55. In other words, FIG. 56shows a structure wherein a transparent light guiding plate 94 which hasa light source 71 on the side face, is bonded with a substrate where anelement which exhibits scattering characteristics is sealed between thetwo transparent substrates 74 and 76. Specifically, a prism layer 82 isformed between the transparent substrates 74 and 76 made of glass, andthe substrate for scattering, where the liquid crystal layer 80, whichrefractive index status is changed by an electric field is filled, isbonded with the transparent light guiding plate 94 by optical bonding96. In the case of this structure, fabrication of the two transparentsubstrates 74 and 76, where an element which exhibits scatteringcharacteristics is sealed, and fabrication of the light guiding platewith a light source 94, can be separated, so that the fabricationprocess steps are separated each other and improves yield. The glasssubstrates 74 and 76 sandwiching the liquid crystal layer 80 are thin,0.5-0.7 mm for example, and the plate thickness of the transparent lightguiding plate 94, where the light source 71 is disposed, is thicker, soas to improve the light entering efficiency from the light source.

The front light structure of the present embodiment does not havescattering characteristics during normal use when the light source isnot turned on, and the illumination light from the light source isscattered and entered to the reflection type liquid crystal displaypanel side only when the light source is turned on for use in a darkplace. Therefore, blurred and distorted characters and images on thedisplay screen can be prevented in normal use, and contrast can beimproved. Also a bright display screen can be implemented even in a darkplace.

[Modification of Reflection Type Liquid Crystal Display Device withFront Light Structure]

In the present embodiment, a reflection type liquid crystal displaydevice having a front light structure as an illumination device isdescribed.

FIG. 102 is a cross-sectional view depicting a reflection type liquidcrystal display panel comprising a conventional front light structure. Apolarizer 504 is formed on the surface of a liquid crystal panel 505,which has a reflection film and a liquid crystal layer inside, and afront light structure comprised of a light source 501, reflector 502 anda light guiding plate 503, is layered on the front. An air layerintervenes between the polarizer 504 and the light guiding plate 503.

Light from the light source enters the light guiding plate 503 asincident light 507A, which has some degree of spreading. The lightguiding plate 503 is a prism where a sharp slope 503A and a mild slope503B are combined, and the incident light 507A is guided in the lightguiding plate 503 while being totally reflected on the mild slope 503Band the face 503C at the liquid crystal panel side. This light, which istotally reflected on the mild slope 503B, is also totally reflected onthe shape slope 503A, advances to the liquid crystal panel 505 side, isreflected on the reflection face in the liquid crystal panel, and isemitted to the display side as light 507P. By this light 507P, thereflection type liquid crystal display panel can be used in a darkpalace with no external light.

Actually however, reflection occurs at the interface 503C between thelight guiding plate 503 and the air layer, or at the interface 504Bbetween the polarizer 504 and the air layer, and the light 507Q, whichdoes not transmit to the liquid crystal panel 505, leaks to the displayside. Also, the light reflected at the sharp slop 503A of the lightguiding plate 503 reflects on the interfaces 503C and 504B. It is alsopossible that light reflected inside the liquid crystal panel 505reflects again on the interfaces 503C and 504B, reflects inside theliquid crystal panel 505, and this light 507S becomes the cause of aghost image on the display. Normal external light also reflects on theinterfaces 503C and 504B without transmitting to the liquid crystalpanel 505, and leaks to the display side as light 507V.

In this way, in the case of a reflection type liquid crystal displaypanel with a conventional front light structure, there are manyreflected light components which do not transmit to the liquid crystalpanel and do not contribute to the display, therefore contrast dropsconsiderably.

Therefore it is a first feature of the present embodiment that a lowrefractive index material, which can be formed at low cost, is disposedbetween the light guiding plate and the polarizer of the front light, sothat normal light components which enter the liquid crystal panel arenot reflected to the display side, while maintaining the light guidingcomponents.

It is a second feature that a low refractive index material, which canbe formed at low cost, is disposed between the touch panel and the lightguiding plate of the front light, so that guided light does not enterthe transparent conductive film while sufficiently controllingreflectance.

It is a third feature that a light shielding layer is formed at thesharp slope side of the prism faces of the light guiding plate via a lowrefractive index layer, so that leak light can be blocked withoutdamaging the functions of the light guiding plate.

CONCRETE CONFIGURATION EXAMPLE Fabrication Example 1

FIG. 90 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabricationexample 1. This example has the above mentioned first feature where 501is a cold cathode tube, 502 is a reflector, 503 is a light guidingplate, 504 is a circular polarizer, 505 is a reflection type liquidcrystal panel, and 506 is a low refractive index layer.

The light guiding plate 503 is fabricated by press-molding acrylic resinwith refractive index n=1.49. The surface of the light guiding plate 503is comprised of a first inclined face 503B, which rises from a flatplane, or from a plane in parallel with the flat plane at a first angle,and a second inclined face 503A, which is adjacent to the first inclinedface 503B, and which falls at a second angle which is larger than thefirst angle. As FIG. 90 shows, the incident face 503D and the plane 503C(the above mentioned flat plane) are almost perpendicular to each other,the plane 503C and the first inclined face 503B have a 2° angle, and theplane 503C and the second inclined face 503A have a 45° angle. The plane503C and the first inclined face 503B may be in parallel (0°).

The circular polarizer 504 is comprised of a polarizer and λ/4 plate(returdation film), which are layered from the light guiding plate 503side.

In this example, a low refractive index layer 506, comprised of fluorineresin material, is formed between the light guiding plate 503 and thepolarizer 504 of the liquid crystal panel, so that the light guidingplate 503, the polarizer 504, and the liquid crystal panel 505 areintegrated without intervening with the air layer. For the lowrefractive index layer 506 comprised of fluorine resin material, a sitopmade by Asahi Glass, for example, is used, and this material hasrefractive index n=1.34. This fluorine resin material can be formedsimply at low cost by dipping the press-molded light guiding plate 503made of acrylic resin into a liquid material tank. This requires a muchlower cost compared with the conventional fabrication method ofAR-coating by a sputtering method, which has been proposed.

Light emitted from the cold cathode ray tube 501 enters the incidentface 503D of the light guiding plate 503 via the reflector 502. Light507A, which entered the light guiding plate, advances inside the lightguiding plate as light which is ±42° with respect to the normal line ofthe platen 503D, that is, with respect to plane 503C. Of this light, thecomponents which entered the mild slope 503B are totally reflected, andbecomes components 507B and 507C which advance to the sharp slope 503Aand the interface 503C. Light 507B is also totally reflected on thesharp slope 503A, and advances to the liquid crystal panel 505 almostvertically. In this case, the low refractive index layer 506 (n=1.34)has been formed between the interface 503C of the light guiding plate503 and the interface 504B of the polarizer 504, so reflected light atthese interfaces is considerably decreased, and most of the componentsadvancing vertically enter the liquid crystal panel 505, and becomelight components to be used for the display. As a result contrastimproves.

With the light 503C, components having an incident angle to theinterface 503C of 64° or more are totally reflected and advance insidethe light guiding plate again. With the light 507A, components advancingdirectly to the interface 503C are equivalent to the light 507C, so areseparated into components which are guided according to the incidentangle and components which enter the liquid crystal panel 505.Therefore, even if the low refractive index layer 506 (n=1.34) isdisposed at the interface 503C of the light guiding plate 503 instead ofa conventional air layer (n=1), the light guiding functions of the lightguiding plate 503 are affected very little, and it is restrained that alight in the light guiding plate leaks to the display without enteringthe liquid crystal panel, and contrast drops.

Out of the components of the incident light advancing directly to theinterface 503C, the components of light which incident angle to theinterface 503C is 64° or less enter the liquid crystal panel 505 via thelow refractive index layer 506 and the circular polarizer 504. Thereare, however, few such components. And these components become straylight due to the characteristics of the liquid crystal panel andpolarizer, and do not contribute to the display.

External illumination light 507D enters from the light guiding plate503, and illuminate the liquid crystal panel 505, but the light guidingplate 503, circular polarizer 504 and reflection liquid crystal panel505 contact each other via the low refractive index layer 506. Since therefractive index of the low refractive index layer 506 is n=1.34, whichis higher than the air layer, n=1, reflectance can be decreased at theinterface. Therefore reflection by the light guiding plate interface503C and the polarizer interface 504B, which have been a problem ofconventional structures, can be considerably decreased. Therefore in thecase of the liquid crystal panel used for this fabrication example,contrast improved dramatically, that is, when only a liquid crystalpanel is used, contrast is 20, when the front light of a conventionalstructure is used, contrast is 5, and when the front light of thepresent invention is used, contrast is 12.

Fabrication Example 2

FIG. 91 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example2. This device also has the above mentioned first feature, and in FIG.91, the same elements as the fabrication example 1 are denoted with thesame numbers, and descriptions for this are omitted.

In the fabrication example 1, interface reflection is controlled bycontacting all the elements, but in the present fabrication example, thelight guiding plate part and the liquid crystal panel pair areseparated, and an effect similar to the fabrication example 1 can beobtained.

As illustrated, the circular polarizer 504 is contacted with the lightguiding plate 503 via the low refractive index layer 506. At this part,the light guiding functions and the reflectance control functions arethe same as the fabrication example 1. However, the light component507B, which emits from the light guiding plate at an angle close tovertical after reflecting to the interface 503A, and the illuminationcomponent 507D from the outside, have reflection components just likeprior art due to the air layer in between when transmitting the circularpolarizer interface 504B and the liquid crystal panel interface 505A.

However, in the present fabrication example, both the lights of theinterfaces 507B and 507D transmit through the circular polarizer, thenare reflected on the interfaces 504B and 505A, and enter the circularpolarizer 504 again. At this time, incident light, which enters thecircular polarizer 504 again, is absorbed by the circular polarizer, soreflected light is not leaked to the display side, and contrast does notdrop as in prior art.

In the present fabrication example, a circular polarizer is used, whichis a polarizer and the λ/4 plate (returdation film) which are bonded.For the λ/4 plate (returdation film), a normal λ/4 plate (returdationfilm) and λ/2 plate (returdation film) may be combined. In this case,combining is more effective since the tolerance, wavelength dependencyand incident angle dependency of a λ/4 plate (returdation film) can becompensated by the λ/2 plate (returdation film).

Fabrication Example 3

FIG. 92 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example3. This example has the above mentioned second feature.

In this example, a transparent conductive film 508 is formed on theentire surface of the light guiding plate 503. In this transparentconductive film 508, a terminal for measuring potential is attached at aperipheral part (not illustrated), so as to function as a touch panel toperform coordinate input based on the potential change at each point.Details on the operation and principle of this touch panel are omittedhere, since it is not related to the principle of the present invention.Other elements are almost the same as the fabrication example 1, and aredenoted with the same numbers as the fabrication example 1, sodescriptions thereof are omitted.

A problem when the touch panel and the reflection liquid crystal displaydevice are integrated is that light in a specific band of the light,which is guided by the light guiding plate, is absorbed by thetransparent conductive film 508. In other words, the transparentconductive film 508 absorbs the light components of blue and red, andgreen becomes dominant on the display face. However, both the lightguiding plate of the front light and the touch panel must be disposed onthe liquid crystal panel (observer side), and cannot have an opticallyindependent configuration, in order to prevent a drop in displayquality.

The present inventors examined structures where the reflection ofdisplay light and the external illumination light are controlled, wherelight which is reflected and advances in the light guiding plate doesnot pass the transparent conductive film, and they invented the presentinvention to dispose the low refractive index layer 506A contactingbetween the light guiding plate 503 and the transparent conductive film508, just like fabrication examples 1 and 2. By using this structure,reflection by display light and external illumination light can berestrained while maintaining the light guiding components.

In the present fabrication example, the low refractive index layer 506Ais formed on the light guiding plate 503 by fluorine resin coating, thenITO film is formed by deposition so as to form the transparent electrodefilm 508. In the light guiding plate fabricated this way, componentswhich entered from the light source to the light guiding plate partiallypass through the low refractive index layer 506A, and reach the ITOlayer 508. However, most components totally reflect at the interfacebetween the light guiding plate 503 and the low refractive index layer506A. Therefore the light components which leak to the ITO layer 508,which is the transparent electrode, decrease, and the conventionalproblem of absorbing blue and red light components in the ITO layer 508is considerably improved, and the integration of the front light and thetouch panel becomes possible.

In the case of a large display device, however, the absorption of blueand red components in the ITO film may be a problem, even with theconfiguration of the present fabrication example. This is because a partof the light which enters from the light source, as mentioned above,passes through the interface 503A, and reaches the ITO layer 508.Therefore the present inventors invented the following configuration asa countermeasure thereof. FIG. 93 shows an example.

As FIG. 93 shows, a dye layer 511 is intervened between the lowrefractive index layer 506A and the transparent electrode layer 508. Theother parts are the same as FIG. 92. The dye layer 511 is contactedbetween the low refractive index layer 506A and the transparentconductive film layer 508, as illustrated. Since the ITO layer 508,which is the transparent electrode layer, absorbs 15% of the B band and25% of the R band, the material of the dye layer 511 is selected tocompensate this, to absorb 25% of the G band and 5-10% of the B band. Bythis, the components of all the RGB bands can be equally absorbed by thedye layer 511 and the ITO layer 508. Therefore green dominating thedisplay face can be prevented. By this structure, the light reaching thetransparent conductive film layer can be corrected by the dye layer,even if color balance is lost by the absorption of the transparentconductive film, the lost balance can be compensated by the dye layer511, and a large touch panel integrated type display device can beimplemented without dropping the display quality.

The front light of the touch panel integrated type can exhibit higherdisplay quality by integrated with a circular polarizer and liquidcrystal panel, just like the fabrication example 1 and 2.

Needless to say, a reflection film type touch panel is possible if aspacer and counter ITO substrates are added.

Fabrication Example 4

FIG. 94 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example4. This example as well has the above mentioned second features.However, this example can be fabricated more easily than the fabricationexample 3.

In this example, the transparent electrode layer and low refractiveindex layer to be formed on the front face side of the light guidingplate 503 is formed by gluing a transparent PET film 509, where the ITOlayer 508 has been deposited in advance, on the surface of the lightguiding plate 503 by a sealing type glue with refractive index n=1.3. InFIG. 94, the ITO layer 508 is deposited on the PET film 509, and thesealing type glue with refractive index 1.3 (hereafter low refractiveindex glue) is coated on the entire surface at the opposite side of theITO layer 508 of the PET film 509. If this PET film is glued on thefront face side of the light guiding plate 503, the PET film 509 and theinterface 503B contact via the low refractive index glue 506A, since theinterface 503B is almost horizontal, as mentioned above.

Since the interface 503A has a sharp slope where height changes rapidly,the PET film cannot be contacted as tightly as the interface 503B, so anair gap (air layer) enters between the interface 503A of the lightguiding plate 503 and the low refractive index layer 506A. Because ofthis, more light reflects on the interface 503A between the acrylicmaterial (n=1.5) of the light guiding plate 503 and the air layer (n=1),compared with the case when PET film is contacted with the lowrefractive index layer 506A, so the light of the light guiding plate 503can be distributed to the liquid crystal panel 505 side moreefficiently.

After forming the ITO layer 508 on the flat PET film 509, the PET filmis simply glued to the light guiding plate 503, so compared with themethod of depositing the ITO layer 509 on the surface of the lightguiding plate 503, this process is simple, and process yield improves.

Fabrication Example 5

FIG. 95A is a cross-sectional view depicting a rough configuration ofthe reflection liquid crystal display device of the fabrication example5. This example is related to the above mentioned third feature. Asillustrated, the low refractive index layer 506A is formed on the PETfilm 509, then a light shielding layer 510 is formed, and these areglued on the surface of the light guiding plate 503. Other parts are thesame as the above mentioned fabrication examples, for which descriptionsare omitted.

As FIG. 101 shows, if the light shielding layer 510 is disposed at theinterface 503A on the light guiding plate 503 via the low refractiveindex layer 506A, patterning by oblique exposure is required to form thelight shielding layer 510. In this fabrication method, the lightshielding layer 510 can be accurately formed, but this fabrication takestime, which increases cost. Therefore the present fabrication examplewas invented as a method of obtaining a similar effect at low cost.

In this fabrication example, PET film is glued, just like in fabricationexample 4, as a means of disposing the light shielding layer 510 via thelow refractive index layer 506A.

FIG. 95B shows a cross-sectional view of the PET film. On the PET film509, the low refractive index bonding layer 506A and the light shieldinglayer 510 are formed sequentially. The light shielding layer 510 isblack ink formed by printing. Unlike conventional inventions, the lightshielding film 510 is formed on the plane of the PET film 509, so aconventional printing method can be used. This sheet is bonded on thelight guiding plate 503. At this time, an alignment step is required sothat the light shielding layer 510 positions on the interface 503A, herecost is lower since this alignment is implemented in a very short timewith simple equipment compared with the conventional oblique exposureand patterning processes.

As illustrated, the light shielding layer 510 and the interface 503A donot contact each other, but an air layer exists between them. Thereforelight which entered the interface 503A is distributed to the liquidcrystal panel 505 side by total reflection, just like the case of aconventional front light. The leak light component, which transmitsthrough the interface 503A, enters the light shielding layer 510 afteremitting from the interface 503A, and is absorbed, so the problem ofleak light emitted to the observer side and dropping the display qualitycan be prevented. Display light reflected from the liquid crystal panel505 is also shielded, but the size of the slope 503A differs 30 times ormore from the slope 503B, so this is hardly a problem. From an observerview, the light shielding layer 510 exists only in a very small area,which does not attract the attention of an observer, and the lightshielding layer also functions to decrease black brightness, so contrastcan be improved.

For the light shielding layer 510, a reflector, absorber or the layersof the reflection layer and absorption layer can be used. If a reflectoris used for the light shielding layer 510, conventional leak light canbe recycled as illumination light to the display panel 505, which canmake the display brighter. In the case of a layered structure, where thereflection layer is disposed at the front face side of the light guidingplate 503 and the absorption layer at the observer side, leak light fromthe light guiding plate is reflected to the liquid crystal panel side,and light from the outside is absorbed, so both a bright display andhigh contrast are implemented at the same time, which is very effective.In these cases as well, these effects can be implemented merely bychanging the ink to be printed, according to the method of the presentfabrication example.

Fabrication Example 6

FIG. 96 is a cross-sectional view depicting a rough configuration of thereflection type liquid crystal display device of the fabrication example6. In this example, a slit type scattering layer 512 is intervenedbetween the light source 501 and the light guiding plate 503, so thatthe angle of the incident light become more parallel with the interface503C. Other parts are the same as the previous fabrication examples, forwhich descriptions are omitted. In the fabrication example 1, a part ofthe components of the light entered from the light guiding plateincident face 503D are not guided but are emitted to the polarizer 504side. These components do not aggravate the display quality very much,as described above, but are wasted as stray light, so this makes theillumination system less efficient, and which becomes a problemespecially when power consumption must be decreased.

Therefore in the present fabrication example, light to enter the lightguiding plate is shaped to be parallel with the interface 503C by theslit type scattering layer 512, so as to improve the efficiency of thelights.

As illustrated, the slit type scattering layer 512 is comprised of ascattering layer 512A where TiO₂ particles are dispersed in acrylicresin and a transparent acrylic resin layer 512B, which are layeredalternately, and transforms the light entered from the interface 503D tolight which has many components heading in the right direction in FIG.96. In other words, the incident light is scattered by the scatteringlayer 512A, and only components parallel with the interface 503Ctransmit through the acrylic layer 512B.

By this, components which are not totally reflected by the interface503C of the light guiding plate 503 but are transmitted in conventionalstructure, can be transformed to components which can be totallyreflected, and the efficiency of the light source improves.

As FIG. 97 shows, this configuration can also be implemented by astructure where the slit type scattering layer 512 is disposed withoutcontacting the incident face 503D of the light guiding plate 503.Instead of the slit type scattering layer, the scattering directivityelement shown in FIG. 98 may be disposed. In this case, the scatteringdirectivity element is disposed to the air, and light enters theincident face 503D of the light guiding plate 503 after directivity isintensified, so the addition of the above mentioned directivity elementcan be smaller, which can make the structure simpler.

FIG. 98 shows an example of a cross-section of the scatteringdirectivity element. This is formed by printing TiO₂ particles 512A onthe acrylic resin layer 512B. The cross-sectional structure of theprinted particle layer 512A has a smooth convex shape, as illustrated.The light entered from the acrylic resin layer 512B is scattered by theparticles 512A, and is emitted to the light guiding plate side asparallel lights.

The incident side shape of the light guiding plate 503 can betransformed to be like 503E, as shown in FIG. 99. Components which arenot totally reflected at the interface 503C between the light guidingplate 503 and the low refractive index layer 506, but which aretransmitted through, are components which incident angle with respect tothe bottom face of the light guiding plate 503C is small. Thereforethese components enter the interface 503C and 503B at locations near thelight source. If this interface has a shape which broadens, as shown inFIG. 503E, the lights after reflection have angles close to beingparallel to the interface 503C. Therefore by appropriately arrangingthis broadening shaped part, the incident light to the light guidingplate 503 can be transformed to be light which have less components,which transmit through the low refractive index layer 506.

Just like the above mentioned fabrication examples, it is not alwaysnecessary to integrate the light guiding plate in this structure. Forexample, as FIG. 100 shows, the broadening shaped part 515 can bedisposed at the incident side of the light guiding plate 503.

As described above, according to the present embodiment, a large effectcan be presented to improve the performance of the reflection liquidcrystal panel with a front light.

As described above, according to the present invention, the undulationfor reflection of the reflection type liquid crystal display device canbe formed by a simple process, and an inclined face distribution ofdesired undulation can be formed with good controllability. Alsoaccording to the present invention, optimum inclined face distributionby undulation for reflection can be obtained, which improvesreflectance.

A method of manufacturing a substrate for a liquid-crystal displaydevice according to an embodiment of the present invention and a methodof manufacturing a liquid-crystal display device using this aredescribed with reference to FIG. 103 to FIG. 110. First of all, thediagrammatic construction of a liquid-crystal display device of thereflective type manufactured using the method of manufacturing aliquid-crystal display device according to this embodiment will bedescribed with reference to FIG. 103. As shown in FIG. 103, thereflective type liquid-crystal display device has a construction inwhich a TFT substrate 2 wherein reflective electrodes comprising opticalreflective material or thin-film transistors (TFTs) or the likeconstituting switching elements were formed in each pixel region, and anopposing substrate 604 formed for example with a color filter (CF) layeror common electrode are stuck together facing each other withliquid-crystal sealed therebetween. An alignment film that aligns theliquid-crystal molecules in a prescribed direction is formed on thefacing surfaces of the two substrates 602 and 604.

For the TFT substrate 602, there are provided a gate bus line drivecircuit 680 on which is mounted a driver IC that drives a plurality ofgate bus lines and a drain bus line drive circuit 682 on which ismounted a driver IC that drives a plurality of drain bus lines. Thedrive circuits 680, 682 are arranged to output scanning signals or datasignals to gate bus lines or drain bus lines, under the control ofprescribed signals that are output from a control circuit 684. Aprescribed polarizing plate 686 is stuck onto the surface on theopposite side to that of the CF layer forming face of the opposingsubstrate 604.

Next, the construction of a TFT substrate manufactured using the methodof manufacture of a substrate for a liquid-crystal display deviceaccording to the present embodiment will be described with reference toFIG. 104 to FIG. 106. FIG. 104 shows the construction of three pixelsand the vicinity thereof of the TFT substrate. FIG. 105 is across-sectional view of the TFT substrate sectioned along the line A-Aof FIG. 104. FIG. 106 is a photomicrograph of six pixels of the TFTsubstrate and the vicinity thereof. As shown in FIG. 104 to FIG. 106,gate bus lines 612 are formed that extend in the left/right direction ofFIG. 104, on a glass substrate 610 of the TFT substrate 602. Aninsulating film 630 is formed on the entire surface of the substrate onthe gate bus line 612. Drain bus lines 614 are formed intersecting thegate bus lines 612 with an insulating film 630 therebetween andextending in the vertical direction of FIG. 104. The TFTs 620 are formedin the vicinity of the positions of intersection of the gate bus lines612 and drain bus lines 614. A TFT 620 comprises an active semiconductorlayer 631 made of for example an a-Si (amorphous silicon) layer on topof an insulating film 630. A channel protecting film 623 is formed ontop of the active semiconductor layer 631. Drain electrodes 621extending from the adjacent drain bus line 614 and source electrodes 622are formed facing each other with a prescribed gap on the channelprotecting film 623. In such a construction, a gate bus line 612directly below the channel protecting film 623 functions as the gateelectrode of the TFT 620.

An inter-layer insulating film (underlayer) 632 comprising for example anovolac type positive resist is formed on the entire surface of thesubstrate on the TFT 620. Wrinkle-shaped undulations (or micro grooves)are formed in the surface of the inter-layer insulating film 632. Areflective electrode 616 comprising an optically reflective material isformed in each pixel region on the inter-layer insulating film 632.Wrinkle-shaped undulations imitating the surface shape of theinter-layer insulating film 632 are formed in the surface of thereflective electrode and 616. The optical scattering characteristics ofthe reflective electrode 616 are improved by the wrinkle-shaped theundulations in the surface, so that incident external light is scatteredand reflected in all directions. The reflective electrode 616 iselectrically connected with a source electrode 622 through a contacthole 624 formed by an aperture of the inter-layer insulating film 632 onthe source electrode 622 of the TFT 620. Also, the reflective electrode616 is arranged so as to cover the adjacent gate bus line 612 at thebottom of FIG. 104.

Also, accumulated capacity bus lines 618 that run transversely acrossthe pixel regions are formed parallel with the gate bus lines 612.Accumulated capacity electrodes (intermediate electrodes) 619 are formedfor each pixel region, with insulating film 630 therebetween, on theaccumulated capacity bus lines 618. The accumulated capacity electrodes619 are electrically connected with the reflective electrodes 616 bymeans of contact holes 626 that are formed by apertures of theinter-layer insulating film 632 on the accumulated capacity electrodes619.

Next, a substrate for liquid-crystal display device according to thisembodiment and a method of manufacturing a liquid-crystal display deviceusing this will be described with reference to FIG. 107 to FIG. 110.FIG. 107 is a table showing whether or not wrinkle-shaped surfaceundulations are present in the inter-layer insulating film surface (i.e.the surface of the reflective electrode) of a TFT substrate manufacturedwith different treatment conditions in each step, using the method ofmanufacturing a substrate for a liquid-crystal display device accordingto the present embodiment, described below. Under the item “formation ofwrinkle-shaped undulations”, cases in which wrinkle-shaped undulationsare formed in the surface of the inter-layer insulating film 632 overthe entire surface of the substrate are indicated by “O” in the tableshown in FIG. 107 and cases in which wrinkle-shaped the undulations arenot formed in the surface of the inter-layer insulating film 632 areindicated by “x”.

A method of manufacturing a substrate for a liquid-crystal displaydevice according to the present embodiment and a method of manufacturinga liquid-crystal display device using this will now be described withreference to embodiments 1 and 2 and a comparative example. First ofall, a method of manufacturing a substrate for a liquid-crystal displaydevice according to embodiments 1 of this embodiment and a method ofmanufacturing a liquid-crystal display device using this will bedescribed with reference to FIG. 108 and FIG. 110. FIG. 108 to FIG. 110are process cross-sectional views showing a method of manufacturing asubstrate for a liquid-crystal display device according to embodiments1, showing a cross section corresponding to FIG. 105. First of all, asshown in FIG. 108(A), for example aluminum (Al)/titanium (Ti) aredeposited in that order using for example a sputtering method on theentire surface of a glass substrate 610, forming a metallic layer (notshown). Next, a resist pattern (not shown) of prescribed shape is formedon the metallic layer by a photolithographic step using a firstphoto-mask. Using the resist pattern that has thus been formed as anetching mask, the metallic layer is subjected to for example dry etchingand the resist pattern is then peeled off, forming gate bus lines (gateelectrodes) 612.

Simultaneously, the accumulated capacity bus lines 618 (not shown inFIG. 108(A)) are formed.

Next, silicon nitride (SiN)/amorphous silicon (a-Si)/SiN is continuouslydeposited using for example the CVD method on the entire surface of thesubstrate on the gate bus lines 612 forming insulating film 630, a-Silayer 631′ and SiN film 623′. Next, a resist pattern of a prescribedshape (not shown) is formed on the SiN film 623′ by a photolithographicstep. In this photolithographic step, back face exposure in whichexposure is effected from the back face side of the glass substrate 610(underside in FIG. 108(A)) through the gate bus lines 12 and exposureusing a second photo-mask are performed. Next, the SiN film 623′ isetched using the resist pattern that has thus been formed as an etchingmask, the resist pattern is then peeled off, and a channel protectingfilm 623 is formed in self-aligned fashion as shown in FIG. 108(B).

Next, as shown in FIG. 108(C), an n⁺a-Si layer 628′ is formed bydepositing n⁺a-Si, using for example the CVD method, on the entiresubstrate surface on the channel protecting film 623. After this, ametallic layer 621′ is formed by continuous deposition of Ti/Al/Ti usingfor example a sputtering method, on the entire surface of the n⁺a-Silayer 628′.

Next, a resist pattern (not shown) of prescribed shape is formed on themetallic layer 621′ by a photolithographic step using a thirdphoto-mask. Next, for example dry etching of the metallic layer 621′,n⁺a-Si layer 628′ and a-Si layer 631′ is performed as shown in FIG.109(A) using the thus-formed resist pattern as an etching mask. In thisetching, the channel protecting film 623 functions as an etchingstopper. After this, the resist pattern is peeled off to form drainelectrodes 621 and source electrodes 622 made of the metallic layer 621′and the n⁺a-Si layer 628′ therebelow. In this way, a TFT 620 is formed.Simultaneously, the drain bus lines 614 and accumulated capacityelectrodes 619 (neither shown in FIG. 109(A)) are formed.

Next, a photosensitive resin film 632′ is formed by coatingphotosensitive resin such as for example novolac positive resist usingfor example a roll coater onto the entire surface of the substrate onthe drain electrodes 621 and source electrodes 622, as shown in FIG.109(B) (resist application step in FIG. 107). As the novolac positiveresist, for example AZ_AFP751 (manufactured by Clariant Japan) may beemployed. Next, the photosensitive resin layer 632′ is pre-baked for 200seconds at 110° C. using for example a hot plate (pre-baking step inFIG. 107).

Next, as shown in FIG. 109(C), the photosensitive resin layer 632′ isexposed and developed using a stepper, using the fourth photo-mask, toform contact holes 624 on the source electrode 622 (exposure/developmentstep in FIG. 107). Contact holes 626 (not shown in FIG. 109(C)) on theaccumulated capacity electrodes 619 are simultaneously formed. Next,using an oven or the like, post-baking of the photosensitive resin layer632′ is performed for 80 minutes at 135° C. (or above 135° C.) (bakingstep prior to UV (ultraviolet rays) irradiation in FIG. 107). Thephotosensitive resin layer 632′ is converted to a semi-hardenedcondition by the pre-baking step and the baking step prior to UVirradiation. The film thickness of the photosensitive resin layer 632′is then for example 3.5 μm.

Next, as shown in FIG. 110(A), UV of wavelength 254 nm is directed ontothe photosensitive resin layer 632′ from the upper surface side thereof(upper part of FIG. 110(A)), using for example a medium high pressuremercury lamp (UV irradiation step in FIG. 107). The illuminance (theirradiation energy density) of the UV is 65 mW/cm² and the irradiationtime is 40 seconds. Consequently, the cumulative irradiation energydensity (cumulative irradiation dose) is about 2600 mJ/cm². Thesubstrate temperature that is thereby attained is no more than 60° C. UVirradiation produces a cross-linking reaction in the surface of thephotosensitive resin layer 632′, as a result of which this layer isselectively reformed (surface cross-linking).

Next, the photosensitive resin layer 632′ is subjected to heat treatmentfor 60 minutes at 215° C., using an oven or the like (annealing step inFIG. 107). A difference is produced in the rate of heat absorptionbetween the surface region of the photosensitive resin layer 632′ thathas been selectively reformed and the lower layer region other than thesurface region, which has not been reformed, so, as shown in FIG.110(B), an inter-layer insulating film 632 is obtained in whichwrinkle-shaped undulations are formed in the surface. It should be notedthat even if no baking step prior to UV irradiation is performed, aninter-layer insulating film 632 is still obtained in whichwrinkle-shaped undulations are formed in the surface.

Next, ashing treatment is performed and this is followed by formation ofa metallic layer (not shown) by deposition of for example Al on theentire surface of the inter-layer insulating film 632, using for examplea sputtering method. Next, a resist pattern (not shown) of a prescribedshape is formed on the metallic layer by a photolithographic step, usinga fifth photo-mask. The metallic layer is etched using the thus-formedresist pattern as an etching mask and the resist pattern is then peeledoff, to form reflective electrodes 616. Wrinkle-shaped the undulationsimitating the surface shape of the inter-layer insulating film 632 areformed in the surface of the reflective electrode 616. The TFT substrate602 shown in FIG. 105 is completed by the above steps.

After this, the TFT substrate 602 and the counter substrate 604 that hasbeen manufactured by separate steps are stuck together and theliquid-crystal display device is thus completed by sealing inliquid-crystal between the two substrates 602 and 604.

Next, a method of manufacturing a substrate for a liquid-crystal displaydevice according to a comparative example of the embodiment will bedescribed with reference to FIG. 107, FIG. 109 and FIG. 110. The stepsup to formation of the TFTs 20 are the same as in embodiment 1, sofurther description thereof is dispensed with. A photosensitive resinlayer 632′ is formed by coating photosensitive resin such as for examplenovolac positive resist using a roll coater or the like over the entiresubstrate surface on the drain electrodes 621 and source electrodes 622of the TFT 620 (resistor application step in FIG. 107). As the novolacpositive resist, for example AZ_AFP751 (manufactured by Clariant Japan)may be employed.

Next, the photosensitive resin layer 632′ is pre-baked for 200 secondsat 110° C. using for example a hot plate (pre-baking step in FIG. 107).

Next, the photosensitive resin layer 632′ is developed by exposing usinga stepper, using the fourth photo-mask of FIG. 106, to form contactholes 624 on the source electrodes 622 (exposure/development step inFIG. 107). Contact holes 626 on the accumulated capacity electrodes 619are simultaneously formed. Next, using an oven or the like, post-bakingof the photosensitive resin layer 632′ is performed for 80 minutes at135° C. (baking step prior to irradiation with UV in FIG. 107). Thephotosensitive resin layer 632′ is converted to a semi-hardenedcondition by the pre-baking step and the baking step prior to UVirradiation. The film thickness of the photosensitive resin layer 632′is then for example 3.5 μm.

Next, UV of wavelength 254 nm is directed onto the photosensitive resinlayer 632′ using for example a high pressure mercury lamp (UVirradiation step in FIG. 107). The illuminance is 12 mW/cm² and theirradiation time 217 seconds. Consequently, the accumulated irradiationenergy density is about 2600 mJ/cm², which is the same as in the UVirradiation step of embodiment 1. The substrate temperature that wasthereby attained was no more than 60° C.

Next, the photosensitive resin layer 632′ is subjected to heat treatmentfor 60 minutes at 215° C., using an oven or the like (annealing step inFIG. 107). However, in contrast to the embodiment 1, no wrinkle-shapedsurface undulations are formed in the surface of the photosensitiveresin layer 632′ over the entire surface of the substrate, so aninter-layer insulating film 632 as shown in FIG. 110(B) over the entiresurface of substrate could not be obtained.

Table 8 shows whether or not wrinkle-shaped surface undulations arepresent in the inter-layer insulating film surface when the irradiationtime in the UV irradiation step in this comparative example is varied.As shown in Table 8, even if the UV irradiation time is varied from 5seconds to 440 seconds, an inter-layer insulating film 632 formed withwrinkle-shaped surface the undulations as shown in FIG. 110(B) over theentire substrate surface is not obtained.

TABLE 8 Cumulative Irradiation irradiation Formation of time dosewrinkle-shaped (sec) (mJ/cm²) surface undulations 5 60 X 15 180 X 30 360X 45 540 X 60 720 X 90 900 X 105 1260 X 217 2600 X 330 3960 X 440 5280 X

Next, a method of manufacturing a substrate for a liquid-crystal displaydevice according to an embodiment 2 will be described. Considering that,in view of the embodiment 1 and the comparative example, formation ofthe wrinkle-shaped surface undulations relates to the state of hardeningof the photosensitive resin layer 632′ prior to UV irradiation, it isdecided, in this embodiment 2, not to harden so much the photosensitiveresin layer 632′, but to make the luminance of UV irradiation lower, 12mW/cm². Specifically, as the baking treatment of the photosensitiveresin layer 632′ prior to UV irradiation, only the pre-baking step ofFIG. 107 is employed, the baking step prior to UV irradiation is notemployed, and, in addition, the pre-baking temperature of thispre-baking step is lowered. A specific description of this embodiment 2is given below with reference to FIG. 107, FIG. 109 and FIG. 110. Itshould be noted that, since the steps up to formation of the TFT 20 arethe same as in the case of the embodiment 1, further description thereofis dispensed with.

A photosensitive resin film 632′ is formed by coating photosensitiveresin such as for example novolac positive resist using for example aroll coater onto the entire surface of the substrate on the drainelectrodes 621 and source electrodes 622 of the TFT 620 (resistapplication step of FIG. 107). As the novolac positive resist, forexample AZ_AFP751 (manufactured by Clariant Japan) may be employed.Next, the pre-baking step in FIG. 107 was performed. Table 2 shows thepre-baking temperature of the pre-baking step. In the pre-baking step,photosensitive resin layers 632′ of a plurality of substrates arerespectively pre-baked for 200 seconds at various pre-bakingtemperatures of 70° C. to 130° C. shown in Table 9 using a hot plate forexample. The photosensitive resin layers 632′ are converted to asemi-hardened condition by the pre-baking step. However, thephotosensitive layer 32′ of the embodiment 2 is not harden to the samedegree as that of the photosensitive resin layer 632′ after the stepprior to UV irradiation in the embodiment 1 and the comparative example.

TABLE 9 Pre-baking Formation of wrinkle-shaped temperature (° C.)surface undulations 70 X 80 ◯ 90 ◯ 100 ◯ 110 ◯ 120 ◯ 130 ◯

Next, the photosensitive resin layer 632′ is exposed and developed usinga stepper, using the fourth photo-mask, to form contact holes 624(exposure/development step in FIG. 107). The film thickness of thephotosensitive resin layer 632′ is then for example 3.5 μm. It should benoted that the baking step prior to UV irradiation of FIG. 107 is notcarried out for the embodiment 2 in order not to harden thephotosensitive resin layer 632′.

Next, the photosensitive resin layer 632′ is irradiated with UV ofwavelength 254 nm, using a high pressure mercury lamp or the like (UVirradiation step in FIG. 107). The illuminance is 12 mW/cm² and theirradiation time 217 seconds. Consequently, the cumulative irradiationenergy density (cumulative irradiation dose) is about 2600 mJ/cm². Thesubstrate temperature in this UV irradiation is no more than 60° C.

Next, the photosensitive resin layer 632′ is subjected to heat treatmentfor 60 minutes at 215° C., using an oven or the like (annealing step inFIG. 107). As a result, as shown in Table 2, even though the irradiationenergy density (illuminance) is lower, such as 12 mW/cm², wrinkle-shapedsurface undulations are formed in the surface of the photosensitiveresin layer 632′ that has been subjected to pre-baking with a pre-bakingtemperature of at least 80° C. (but no more than 130° C.), and aninter-layer insulating film 632 having the undulations as shown in FIG.110(B) is thereby obtained. However, wrinkle-shaped surface undulationsare not formed on the entire substrate surface on the surface of aphotosensitive resin layer 632′ that is pre-baked at a pre-bakingtemperature of 70° C. The reason seems to be that the photosensitiveresin layer 632′ is too soft before UV irradiation.

Next, ashing treatment is performed and this is followed by formation ofa metallic layer by deposition of for example Al on the entire surfaceof the inter-layer insulating film 632, using for example a sputteringmethod. Next, a resist pattern of a prescribed shape is formed on themetallic layer by a photolithographic step, using a fifth photo-mask.The metallic layer is etched using the thus-formed resist pattern as anetching mask and the resist pattern is then peeled off, to formreflective electrodes 616. The TFT substrate 602 shown in FIG. 105 iscompleted by the above steps. Wrinkle-shaped surface undulationsimitating the surface shape of the inter-layer insulating film 632 areformed on the entire surface of the reflective electrode 616 of thesubstrate that has been subjected to the pre-baking at a pre-bakingtemperature of at least 80° C. but no more than 130° C. and not to thebaking prior to UV irradiation. Wrinkle-shaped surface undulations arenot formed on the entire surface of the reflective electrode 616 of thesubstrate that is pre-baked with a pre-baking temperature of 70° C.

According to the embodiment 2, even if irradiation of UV is performedusing a comparatively low-illuminance lamp instead of thehigh-illuminance lamp as in the embodiment, wrinkle-shaped surfaceundulations can still be formed in the surface of the reflectiveelectrode 16 over the entire surface thereof by not hardening thephotosensitive resin layer 632′ more than necessary, by relativelylowering the baking temperature of the photosensitive resin layer 32′prior to UV irradiation.

The following conclusions are obtained concerning the conditions forformation of wrinkle-shaped surface undulations in the surface of theinter-layer insulating film 32 over the entire surface, from the aboveembodiments 1 and 2 and the comparative example.

(1) In the UV irradiation step, both the cumulative irradiation dose(the cumulative irradiation energy density (mJ/cm²)) and the illuminance(the irradiation energy density per a second (mW/cm²)) are important.Specifically, UV of a prescribed cumulative irradiation dose is directedonto the photosensitive resin layer 632′ with an illuminance exceeding12 mW/cm². Selective reforming of the surface region of thephotosensitive resin layer 632′ is thereby achieved. That is, the higherilluminance (the higher irradiation energy density per a second)exceeding 12 mW/cm² makes the surface of the photosensitive resin layer632′ being selectively reformed so as to become the undulation, eventhough the resin layer is harden or semi-harden. This is proved by theembodiment 1.(2) In addition to the illuminance in the UV irradiation step, the stateof hardness of the photosensitive resin layer 632′ prior to UVirradiation is important. In particular, if the illuminance of the UV inthe UV irradiation step is comparatively low, the photosensitive resinlayer 632′ prior to UV irradiation must not be made harder thannecessary and must not be made too soft. Specifically, if theilluminance of the UV in the UV irradiation step is 12 mW/cm² or less, astep of baking prior to UV irradiation should not be performed and thepre-baking temperature of the pre-baking step should be made at least80° C. (pre-baking time 200 seconds). This is proved by the embodiment2.

As described above, in this embodiment, compared with the conventionalmethod of manufacturing a TFT substrate, there is no need for a separatedeposition process and there is no need for a new photo-mask. Also, inthis embodiment, there is no need for a special manufacturing device orresin material. Consequently, the manufacturing steps of the TFTsubstrate 2 can be simplified, making it possible to reducemanufacturing costs.

Also, in this embodiment, excellent wrinkle-shaped surface undulationscan easily be formed in the surface of the reflective electrodes 16 ofthe TFT substrate 2. Consequently, excellent surface quality withexcellent optical diffusion characteristics are obtained with areflective type liquid-crystal display device manufactured using thisembodiment.

The present invention is not restricted to the above embodiments but canbe modified in various ways.

For example, although, in the above embodiments, the inter-layerinsulating film 632 is formed using novolac positive resist, the presentinvention is not restricted to this. Negative resist could be employed,and the inter-layer insulating film 632 could be formed using othertypes of photosensitive resin such as acrylic-based resist or the likeor for example other types of resin that do not have photosensitivity.

Also, although, in the above embodiments, the energy is applied to thephotosensitive resin layer 632′ by irradiation with UV light, thepresent invention is not restricted to this and the energy could beapplied from the surface side of the photosensitive resin layer 32′ byanother method such as irradiation with light other than UV light.

Furthermore, although, in the above embodiments, a reflective typeliquid-crystal display device is taken as an example, the presentinvention is not restricted to this and could also be applied to asemi-transparent type liquid-crystal display device.

Also, although, in the above embodiments, the example was given of asubstrate for a liquid-crystal display device comprising TFTs 620 of thechannel protected film type, the present invention is not restricted tothis and could be applied to a substrate for liquid-crystal displaydevices comprising channel etched type TFTs 20.

Furthermore, although in the above embodiments, an active matrix typeliquid-crystal display device is taken as an example, the presentinvention is not restricted to this and could be applied to aliquid-crystal display device of the simple matrix type.

As described above, with the present invention, a liquid-crystal displaydevice can be realized whereby excellent display characteristics can beobtained even though the manufacturing steps are simplified.

1. A method of manufacturing a substrate for a liquid-crystal displaydevice comprising the steps of: coating a resin layer on a substrate,wherein the resin layer can be at least three conditions including anon-harden condition, a semi-harden condition and a harden conditionthrough a heat treatment; performing a first heat treatment to the resinlayer to make the resin layer the harden condition or the semi-hardencondition; applying energy having an energy density per a unit time,which is more than a prescribed value, to the resin layer so as toselectively reform the surface portion of said resin layer and togenerate a difference in a rate of thermal shrinkage between saidsurface portion and the layer portion other than the surface portion;performing a second heat treatment to the resin layer to form wrinklesof micro-grooves in said surface portion; and forming a reflectiveelectrode on said surface portion.
 2. The method of manufacturing asubstrate for a liquid-crystal display device according to the claim 1,wherein, in said first heat treatment, the semi-harden condition is madeby a first pre-bake treatment with from 80 to 130 degrees centigrade,the harden condition is made by the first pre-bake treatment and asecond pre-bake treatment, and the energy having an energy density per aunit time, which is more than a prescribed value, is given by anirradiation of ultra-violet light whose energy density per a unit timeis more than 12 mW/cm².
 3. A method of manufacturing a substrate for aliquid-crystal display device comprising the steps of: coating a resinlayer on a substrate, wherein the resin layer can be at least threeconditions including a non-harden condition, a semi-harden condition anda harden condition through a heat treatment; performing a first heattreatment to the resin layer to make the resin layer the hardencondition; applying energy having an energy density per a unit time,which is no more than 12 mW/cm², to the resin layer so as to selectivelyreform the surface portion of said resin layer and to generate adifference in a rate of thermal shrinkage between said surface portionand the layer portion other than the surface portion; performing asecond heat treatment to the resin layer to form wrinkles ofmicro-grooves in said surface portion; and forming a reflectiveelectrode on said surface portion.
 4. The method of manufacturing asubstrate for a liquid-crystal display device according to the claim 3,wherein, in said first heat treatment, the semi-harden condition is madeby a first pre-bake treatment with from 80 to 130 degrees centigrade.